Queueing and mapping utilities for outbound data sync (#4881)

Add a registry for datasync providers and an associated sync queue, to be used by 
plugins that transfer data from pretix orders to external systems. 
Additionally, provide a generic data mapping interface to be used in settings pages 
of such plugins, to let users configure which information from pretix to fill into
which data fields of the external system.

---------

Co-authored-by: Raphael Michel <michel@rami.io>

doc/development/api/datasync.rst

@@ -0,0 +1,200 @@
+.. highlight:: python
+   :linenothreshold: 5
+
+Data sync providers
+===================
+
+.. warning:: This feature is considered **experimental**. It might change at any time without prior notice.
+
+pretix provides connectivity to many external services through plugins. A common requirement
+is unidirectionally sending (order, customer, ticket, ...) data into external systems.
+The transfer is usually triggered by signals provided by pretix core (e.g. :data:`order_placed`),
+but performed asynchronously.
+
+Such plugins should use the :class:`OutboundSyncProvider` API to utilize the queueing, retry and mapping mechanisms as well as the user interface for configuration and monitoring.
+
+An :class:`OutboundSyncProvider` for registering event participants in a mailing list could start
+like this, for example:
+
+.. code-block:: python
+
+    from pretix.base.datasync.datasync import OutboundSyncProvider
+
+    class MyListSyncProvider(OutboundSyncProvider):
+        identifier = "my_list"
+        display_name = "My Mailing List Service"
+        # ...c
+
+
+The plugin must register listeners in `signals.py` for all signals that should to trigger a sync and
+within it has to call :meth:`MyListSyncProvider.enqueue_order` to enqueue the order for synchronization:
+
+.. code-block:: python
+
+    @receiver(order_placed, dispatch_uid="mylist_order_placed")
+    def on_order_placed(sender, order, **kwargs):
+        MyListSyncProvider.enqueue_order(order, "order_placed")
+
+
+Furthermore, most of these plugins need to translate data from some pretix objects (e.g. orders)
+into an external system's data structures. Sometimes, there is only one reasonable way or the
+plugin author makes an opinionated decision what information from which objects should be
+transferred into which data structures in the external system.
+
+Otherwise, you can use a :class:`PropertyMappingFormSet` to let the user set up a mapping from pretix model fields
+to external data fields. You could store the mapping information either in the event settings, or in a separate
+data model. Your implementation of :attr:`OutboundSyncProvider.mappings`
+needs to provide a list of mappings, which can be e.g. static objects or model instances, as long as they
+have at least the properties defined in
+:class:`pretix.base.datasync.datasync.StaticMapping`.
+
+.. code-block:: python
+
+    # class MyListSyncProvider, contd.
+        def mappings(self):
+            return [
+                StaticMapping(
+                    id=1, pretix_model='Order', external_object_type='Contact',
+                    pretix_id_field='email', external_id_field='email',
+                    property_mappings=self.event.settings.mylist_order_mapping,
+                ))
+            ]
+
+
+Currently, we support `orders` and `order positions` as data sources, with the data fields defined in
+:func:`pretix.base.datasync.sourcefields.get_data_fields`.
+
+To perform the actual sync, implement :func:`sync_object_with_properties` and optionally
+:func:`finalize_sync_order`. The former is called for each object to be created according to the ``mappings``.
+For each order that was enqueued using :func:`enqueue_order`:
+
+- each Mapping with ``pretix_model == "Order"`` results in one call to :func:`sync_object_with_properties`,
+- each Mapping with ``pretix_model == "OrderPosition"`` results in one call to
+  :func:`sync_object_with_properties` per order position,
+- :func:`finalize_sync_order` is called one time after all calls to :func:`sync_object_with_properties`.
+
+
+Implementation examples
+-----------------------
+
+For example implementations, see the test cases in :mod:`tests.base.test_datasync`.
+
+In :class:`SimpleOrderSync`, a basic data transfer of order data only is
+shown. Therein, a ``sync_object_with_properties`` method is defined as follows:
+
+.. code-block:: python
+
+    from pretix.base.datasync.utils import assign_properties
+
+    def sync_object_with_properties(
+            self, external_id_field, id_value, properties: list, inputs: dict,
+            mapping, mapped_objects: dict, **kwargs,
+    ):
+        # First, we query the external service if our object-to-sync already exists there.
+        # This is necessary to make sure our method is idempotent, i.e. handles already synced
+        # data gracefully.
+        pre_existing_object = self.fake_api_client.retrieve_object(
+            mapping.external_object_type,
+            external_id_field,
+            id_value
+        )
+
+        # We use the helper function ``assign_properties`` to update a pre-existing object.
+        update_values = assign_properties(
+            new_values=properties,
+            old_values=pre_existing_object or {},
+            is_new=pre_existing_object is None,
+            list_sep=";",
+        )
+
+        # Then we can send our new data to the external service. The specifics of course depends
+        # on your API, e.g. you may need to use different endpoints for creating or updating an
+        # object, or pass the identifier separately instead of in the same dictionary as the
+        # other properties.
+        result = self.fake_api_client.create_or_update_object(mapping.external_object_type, {
+            **update_values,
+            external_id_field: id_value,
+            "_id": pre_existing_object and pre_existing_object.get("_id"),
+        })
+
+        # Finally, return a dictionary containing at least `object_type`, `external_id_field`,
+        # `id_value`, `external_link_href`, and `external_link_display_name` keys.
+        # Further keys may be provided for your internal use. This dictionary is provided
+        # in following calls in the ``mapped_objects`` dict, to allow creating associations
+        # to this object.
+        return {
+            "object_type": mapping.external_object_type,
+            "external_id_field": external_id_field,
+            "id_value": id_value,
+            "external_link_href": f"https://example.org/external-system/{mapping.external_object_type}/{id_value}/",
+            "external_link_display_name": f"Contact #{id_value} - Jane Doe",
+            "my_result": result,
+        }
+
+.. note:: The result dictionaries of earlier invocations of :func:`sync_object_with_properties` are
+          only provided in subsequent calls of the same sync run, such that a mapping can
+          refer to e.g. the external id of an object created by a preceding mapping.
+          However, the result dictionaries are currently not provided across runs. This will
+          likely change in a future revision of this API, to allow easier integration of external
+          systems that do not allow retrieving/updating data by a pretix-provided key.
+
+``mapped_objects`` is a dictionary of lists of dictionaries. The keys to the dictionary are
+the mapping identifiers (``mapping.id``), the lists contain the result dictionaries returned
+by :func:`sync_object_with_properties`.
+
+
+In :class:`OrderAndTicketAssociationSync`, an example is given where orders, order positions,
+and the association between them are transferred.
+
+
+The OutboundSyncProvider base class
+-----------------------------------
+
+.. autoclass:: pretix.base.datasync.datasync.OutboundSyncProvider
+   :members:
+
+
+Property mapping format
+-----------------------
+
+To allow the user to configure property mappings, you can use the PropertyMappingFormSet,
+which will generate the required ``property_mappings`` value automatically. If you need
+to specify the property mappings programmatically, you can refer to the description below
+on their format.
+
+.. autoclass:: pretix.control.forms.mapping.PropertyMappingFormSet
+   :members: to_property_mappings_json
+
+A simple JSON-serialized ``property_mappings`` list for mapping some order information can look like this:
+
+.. code-block:: json
+
+      [
+        {
+            "pretix_field": "email",
+            "external_field": "orderemail",
+            "value_map": "",
+            "overwrite": "overwrite",
+        },
+        {
+            "pretix_field": "order_status",
+            "external_field": "status",
+            "value_map": "{\"n\": \"pending\", \"p\": \"paid\", \"e\": \"expired\", \"c\": \"canceled\", \"r\": \"refunded\"}",
+            "overwrite": "overwrite",
+        },
+        {
+            "pretix_field": "order_total",
+            "external_field": "total",
+            "value_map": "",
+            "overwrite": "overwrite",
+        }
+      ]
+
+
+Translating mappings on Event copy
+----------------------------------
+
+Property mappings can contain references to event-specific primary keys. Therefore, plugins must register to the
+event_copy_data signal and call translate_property_mappings on all property mappings they store.
+
+.. autofunction:: pretix.base.datasync.utils.translate_property_mappings

doc/development/api/index.rst

@@ -18,5 +18,6 @@ Contents:
    customview
    cookieconsent
    auth
+   datasync
    general
    quality

src/pretix/base/apps.py

@@ -46,7 +46,7 @@ class PretixBaseConfig(AppConfig):
         from . import invoice  # NOQA
         from . import notifications  # NOQA
         from . import email  # NOQA
-        from .services import auth, checkin, currencies, export, mail, tickets, cart, modelimport, orders, invoices, cleanup, update_check, quotas, notifications, vouchers  # NOQA
+        from .services import auth, checkin, currencies, datasync, export, mail, tickets, cart, modelimport, orders, invoices, cleanup, update_check, quotas, notifications, vouchers  # NOQA
         from .models import _transactions  # NOQA
         from django.conf import settings
 

src/pretix/base/datasync/__init__.py

@@ -0,0 +1,21 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#

src/pretix/base/datasync/datasync.py

@@ -0,0 +1,437 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+import json
+import logging
+from collections import namedtuple
+from datetime import timedelta
+from functools import cached_property
+from typing import Optional, Protocol
+
+import sentry_sdk
+from django.db import DatabaseError, transaction
+from django.utils.timezone import now
+from django.utils.translation import gettext_lazy as _
+
+from pretix.base.datasync.sourcefields import (
+    EVENT, EVENT_OR_SUBEVENT, ORDER, ORDER_POSITION, get_data_fields,
+)
+from pretix.base.i18n import language
+from pretix.base.logentrytype_registry import make_link
+from pretix.base.models.datasync import OrderSyncQueue, OrderSyncResult
+from pretix.base.signals import EventPluginRegistry
+from pretix.helpers import OF_SELF
+
+logger = logging.getLogger(__name__)
+
+
+datasync_providers = EventPluginRegistry({"identifier": lambda o: o.identifier})
+
+
+class BaseSyncError(Exception):
+    def __init__(self, messages, full_message=None):
+        self.messages = messages
+        self.full_message = full_message
+
+
+class UnrecoverableSyncError(BaseSyncError):
+    """
+    A SyncProvider encountered a permanent problem, where a retry will not be successful.
+    """
+    failure_mode = "permanent"
+
+
+class SyncConfigError(UnrecoverableSyncError):
+    """
+    A SyncProvider is misconfigured in a way where a retry without configuration change will
+    not be successful.
+    """
+    failure_mode = "config"
+
+
+class RecoverableSyncError(BaseSyncError):
+    """
+    A SyncProvider has encountered a temporary problem, and the sync should be retried
+    at a later time.
+    """
+    pass
+
+
+class ObjectMapping(Protocol):
+    id: int
+    pretix_model: str
+    external_object_type: str
+    pretix_id_field: str
+    external_id_field: str
+    property_mappings: str
+
+
+StaticMapping = namedtuple('StaticMapping', ('id', 'pretix_model', 'external_object_type', 'pretix_id_field', 'external_id_field', 'property_mappings'))
+
+
+class OutboundSyncProvider:
+    max_attempts = 5
+
+    def __init__(self, event):
+        self.event = event
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.close()
+
+    @classmethod
+    @property
+    def display_name(cls):
+        return str(cls.identifier)
+
+    @classmethod
+    def enqueue_order(cls, order, triggered_by, not_before=None):
+        """
+        Adds an order to the sync queue. May only be called on derived classes which define an ``identifier`` attribute.
+
+        Should be called in the appropriate signal receivers, e.g.::
+
+            @receiver(order_placed, dispatch_uid="mysync_order_placed")
+            def on_order_placed(sender, order, **kwargs):
+                MySyncProvider.enqueue_order(order, "order_placed")
+
+        :param order: the Order that should be synced
+        :param triggered_by: the reason why the order should be synced, e.g. name of the signal
+                             (currently only used internally for logging)
+        """
+        if not hasattr(cls, 'identifier'):
+            raise TypeError('Call this method on a derived class that defines an "identifier" attribute.')
+        OrderSyncQueue.objects.update_or_create(
+            order=order,
+            sync_provider=cls.identifier,
+            in_flight=False,
+            defaults={
+                "event": order.event,
+                "triggered_by": triggered_by,
+                "not_before": not_before or now(),
+                "need_manual_retry": None,
+            },
+        )
+
+    @classmethod
+    def get_external_link_info(cls, event, external_link_href, external_link_display_name):
+        return {
+            "href": external_link_href,
+            "val": external_link_display_name,
+        }
+
+    @classmethod
+    def get_external_link_html(cls, event, external_link_href, external_link_display_name):
+        info = cls.get_external_link_info(event, external_link_href, external_link_display_name)
+        return make_link(info, '{val}')
+
+    def next_retry_date(self, sq):
+        """
+        Optionally override to configure a different retry backoff behavior
+        """
+        return now() + timedelta(hours=1)
+
+    def should_sync_order(self, order):
+        """
+        Optionally override this method to exclude certain orders from sync by returning ``False``
+        """
+        return True
+
+    @property
+    def mappings(self):
+        """
+        Implementations must override this property to provide the data mappings as a list of objects.
+
+        They can return instances of the ``StaticMapping`` `namedtuple` defined above, or create their own
+        class (e.g. a Django model).
+
+        :return: The returned objects must have at least the following properties:
+
+                - `id`: Unique identifier for this mapping. If the mappings are Django models, the database primary key
+                  should be used. This may be referenced in other mappings, to establish relations between objects.
+                - `pretix_model`: Which pretix model to use as data source in this mapping. Possible values are
+                  the keys of ``sourcefields.AVAILABLE_MODELS``
+                - `external_object_type`: Destination object type in the target system. opaque string of maximum 128 characters.
+                - `pretix_id_field`: Which pretix data field should be used to identify the mapped object. Any ``DataFieldInfo.key``
+                  returned by ``sourcefields.get_data_fields()`` for the combination of ``Event`` and ``pretix_model``.
+                - `external_id_field`: Destination identifier field in the target system.
+                - `property_mappings`: Mapping configuration as generated by ``PropertyMappingFormSet.to_property_mappings_json()``.
+        """
+        raise NotImplementedError
+
+    def sync_queued_orders(self, queued_orders):
+        """
+        This method should catch all Exceptions and handle them appropriately. It should never throw
+        an Exception, as that may block the entire queue.
+        """
+        for queue_item in queued_orders:
+            with transaction.atomic():
+                try:
+                    sq = (
+                        OrderSyncQueue.objects
+                        .select_for_update(of=OF_SELF, nowait=True)
+                        .select_related("order")
+                        .get(pk=queue_item.pk)
+                    )
+                    if sq.in_flight:
+                        continue
+                    sq.in_flight = True
+                    sq.in_flight_since = now()
+                    sq.save()
+                except DatabaseError:
+                    # Either select_for_update failed to lock the row, or we couldn't set in_flight
+                    # as this order is already in flight (UNIQUE violation). In either case, we ignore
+                    # this order for now.
+                    continue
+
+            try:
+                mapped_objects = self.sync_order(sq.order)
+                if not all(all(not res or res.sync_info.get("action", "") == "nothing_to_do" for res in res_list) for res_list in mapped_objects.values()):
+                    sq.order.log_action("pretix.event.order.data_sync.success", {
+                        "provider": self.identifier,
+                        "objects": {
+                            mapping_id: [osr and osr.to_result_dict() for osr in results]
+                            for mapping_id, results in mapped_objects.items()
+                        },
+                    })
+                sq.delete()
+            except UnrecoverableSyncError as e:
+                sq.set_sync_error(e.failure_mode, e.messages, e.full_message)
+            except RecoverableSyncError as e:
+                sq.failed_attempts += 1
+                sq.not_before = self.next_retry_date(sq)
+                # model changes saved by set_sync_error / clear_in_flight calls below
+                if sq.failed_attempts >= self.max_attempts:
+                    logger.exception('Failed to sync order (max attempts exceeded)')
+                    sentry_sdk.capture_exception(e)
+                    sq.set_sync_error("exceeded", e.messages, e.full_message)
+                else:
+                    logger.info(
+                        f"Could not sync order {sq.order.code} to {type(self).__name__} "
+                        f"(transient error, attempt #{sq.failed_attempts}, next {sq.not_before})",
+                        exc_info=True,
+                    )
+                    sq.clear_in_flight()
+            except Exception as e:
+                logger.exception('Failed to sync order (unhandled exception)')
+                sentry_sdk.capture_exception(e)
+                sq.set_sync_error("internal", [], str(e))
+
+    @cached_property
+    def data_fields(self):
+        return {
+            f.key: f
+            for f in get_data_fields(self.event)
+        }
+
+    def get_field_value(self, inputs, mapping_entry):
+        key = mapping_entry["pretix_field"]
+        try:
+            field = self.data_fields[key]
+        except KeyError:
+            with language(self.event.settings.locale):
+                raise SyncConfigError([_(
+                    'Field "{field_name}" is not valid for {available_inputs}. Please check your {provider_name} settings.'
+                ).format(key=key, available_inputs="/".join(inputs.keys()), provider_name=self.display_name)])
+        input = inputs[field.required_input]
+        val = field.getter(input)
+        if isinstance(val, list):
+            if field.enum_opts and mapping_entry.get("value_map"):
+                map = json.loads(mapping_entry["value_map"])
+                try:
+                    val = [map[el] for el in val]
+                except KeyError:
+                    with language(self.event.settings.locale):
+                        raise SyncConfigError([_(
+                            'Please update value mapping for field "{field_name}" - option "{val}" not assigned'
+                        ).format(field_name=key, val=val)])
+
+            val = ",".join(val)
+        return val
+
+    def get_properties(self, inputs: dict, property_mappings: str):
+        property_mappings = json.loads(property_mappings)
+        return [
+            (m["external_field"], self.get_field_value(inputs, m), m["overwrite"])
+            for m in property_mappings
+        ]
+
+    def sync_object_with_properties(
+            self,
+            external_id_field: str,
+            id_value,
+            properties: list,
+            inputs: dict,
+            mapping: ObjectMapping,
+            mapped_objects: dict,
+            **kwargs,
+    ) -> Optional[dict]:
+        """
+        This method is called for each object that needs to be created/updated in the external system -- which these are is
+        determined by the implementation of the `mapping` property.
+
+        :param external_id_field: Identifier field in the external system as provided in ``mapping.external_identifier``
+        :param id_value: Identifier contents as retrieved from the property specified by ``mapping.pretix_identifier`` of the model
+                         specified by ``mapping.pretix_model``
+        :param properties: All properties defined in ``mapping.property_mappings``, as list of three-tuples
+                           ``(external_field, value, overwrite)``
+        :param inputs: All pretix model instances from which data can be retrieved for this mapping.
+                       Dictionary mapping from sourcefields.ORDER_POSITION, .ORDER, .EVENT, .EVENT_OR_SUBEVENT to the
+                       relevant Django model.
+                       Most providers don't need to use this parameter directly, as `properties` and `id_value`
+                       already contain the values as evaluated from the available inputs.
+        :param mapping: The mapping object as returned by ``self.mappings``
+        :param mapped_objects: Information about objects that were synced in the same sync run, by mapping definitions
+                               *before* the current one in order of ``self.mappings``.
+                               Type is a dictionary ``{mapping.id: [list of OrderSyncResult objects]}``
+                               Useful to create associations between objects in the target system.
+
+        Example code to create return value::
+
+                 return {
+                    # optional:
+                    "action": "nothing_to_do",  # to inform that no action was taken, because the data was already up-to-date.
+                                                # other values for action (e.g. create, update) currently have no special
+                                                # meaning, but are visible for debugging purposes to admins.
+
+                    # optional:
+                    "external_link_href": "https://external-system.example.com/backend/link/to/contact/123/",
+                    "external_link_display_name": "Contact #123 - Jane Doe",
+                    "...optionally further values you need in mapped_objects for association": 123456789,
+                 }
+
+        The return value needs to be a JSON serializable dict, or None.
+
+        Return None only in case you decide this object should not be synced at all in this mapping. Do not return None in
+        case the object is already up-to-date in the target system (return "action": "nothing_to_do" instead).
+
+        This method needs to be idempotent, i.e. calling it multiple times with the same input values should create
+        only a single object in the target system.
+
+        Subsequent calls with the same mapping and id_value should update the existing object, instead of creating a new one.
+        In a SQL database, you might use an `INSERT OR UPDATE` or `UPSERT` statement; many REST APIs provide an equivalent API call.
+        """
+        raise NotImplementedError()
+
+    def sync_object(
+            self,
+            inputs: dict,
+            mapping,
+            mapped_objects: dict,
+    ):
+        logger.debug("Syncing object %r, %r, %r", inputs, mapping, mapped_objects)
+        properties = self.get_properties(inputs, mapping.property_mappings)
+        logger.debug("Properties: %r", properties)
+
+        id_value = self.get_field_value(inputs, {"pretix_field": mapping.pretix_id_field})
+        if not id_value:
+            return None
+
+        info = self.sync_object_with_properties(
+            external_id_field=mapping.external_id_field,
+            id_value=id_value,
+            properties=properties,
+            inputs=inputs,
+            mapping=mapping,
+            mapped_objects=mapped_objects,
+        )
+        if not info:
+            return None
+        external_link_href = info.pop('external_link_href', None)
+        external_link_display_name = info.pop('external_link_display_name', None)
+        obj, created = OrderSyncResult.objects.update_or_create(
+            order=inputs.get(ORDER), order_position=inputs.get(ORDER_POSITION), sync_provider=self.identifier,
+            mapping_id=mapping.id,
+            defaults=dict(
+                external_object_type=mapping.external_object_type,
+                external_id_field=mapping.external_id_field,
+                id_value=id_value,
+                external_link_href=external_link_href,
+                external_link_display_name=external_link_display_name,
+                sync_info=info,
+                transmitted=now(),
+            )
+        )
+        return obj
+
+    def sync_order(self, order):
+        if not self.should_sync_order(order):
+            logger.debug("Skipping order %r", order)
+            return
+
+        logger.debug("Syncing order %r", order)
+        positions = list(
+            order.all_positions
+            .prefetch_related("answers", "answers__question")
+            .select_related(
+                "voucher",
+            )
+        )
+        order_inputs = {ORDER: order, EVENT: self.event}
+        mapped_objects = {}
+        for mapping in self.mappings:
+            if mapping.pretix_model == 'Order':
+                mapped_objects[mapping.id] = [
+                    self.sync_object(order_inputs, mapping, mapped_objects)
+                ]
+            elif mapping.pretix_model == 'OrderPosition':
+                mapped_objects[mapping.id] = [
+                    self.sync_object({
+                        **order_inputs, EVENT_OR_SUBEVENT: op.subevent or self.event, ORDER_POSITION: op
+                    }, mapping, mapped_objects)
+                    for op in positions
+                ]
+            else:
+                raise SyncConfigError("Invalid pretix model '{}'".format(mapping.pretix_model))
+        self.finalize_sync_order(order)
+        return mapped_objects
+
+    def filter_mapped_objects(self, mapped_objects, inputs):
+        """
+        For order positions, only
+        """
+        if ORDER_POSITION in inputs:
+            return {
+                mapping_id: [
+                    osr for osr in results
+                    if osr and (osr.order_position_id is None or osr.order_position_id == inputs[ORDER_POSITION].id)
+                ]
+                for mapping_id, results in mapped_objects.items()
+            }
+        else:
+            return mapped_objects
+
+    def finalize_sync_order(self, order):
+        """
+        Called after ``sync_object`` has been called successfully for all objects of a specific order. Can
+        be used for saving bulk information per order.
+        """
+        pass
+
+    def close(self):
+        """
+        Called after all orders of an event have been synced. Can be used for clean-up tasks (e.g. closing
+        a session).
+        """
+        pass

src/pretix/base/datasync/sourcefields.py

@@ -0,0 +1,534 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+from collections import namedtuple
+from functools import partial
+
+from django.db.models import Max, Q
+from django.utils.translation import gettext_lazy as _
+
+from pretix.base.models import Checkin, InvoiceAddress, Order, Question
+from pretix.base.settings import PERSON_NAME_SCHEMES
+
+
+def get_answer(op, question_identifier=None):
+    a = None
+    if op.addon_to:
+        if "answers" in getattr(op.addon_to, "_prefetched_objects_cache", {}):
+            try:
+                a = [
+                    a
+                    for a in op.addon_to.answers.all()
+                    if a.question.identifier == question_identifier
+                ][0]
+            except IndexError:
+                pass
+        else:
+            a = op.addon_to.answers.filter(
+                question__identifier=question_identifier
+            ).first()
+
+    if "answers" in getattr(op, "_prefetched_objects_cache", {}):
+        try:
+            a = [
+                a
+                for a in op.answers.all()
+                if a.question.identifier == question_identifier
+            ][0]
+        except IndexError:
+            pass
+    else:
+        a = op.answers.filter(question__identifier=question_identifier).first()
+
+    if not a:
+        return ""
+    else:
+        if a.question.type in (Question.TYPE_CHOICE, Question.TYPE_CHOICE_MULTIPLE):
+            return [str(o.identifier) for o in a.options.all()]
+        if a.question.type == Question.TYPE_BOOLEAN:
+            return a.answer == "True"
+        return a.answer
+
+
+def get_payment_date(order):
+    if order.status == Order.STATUS_PENDING:
+        return None
+
+    return isoformat_or_none(order.payments.aggregate(m=Max("payment_date"))["m"])
+
+
+def isoformat_or_none(dt):
+    return dt and dt.isoformat()
+
+
+def first_checkin_on_list(list_pk, position):
+    checkin = position.checkins.filter(
+        list__pk=list_pk, type=Checkin.TYPE_ENTRY
+    ).first()
+    if checkin:
+        return isoformat_or_none(checkin.datetime)
+
+
+def split_name_on_last_space(name, part):
+    name_parts = name.rsplit(" ", 1)
+    return name_parts[part] if len(name_parts) > part else ""
+
+
+ORDER_POSITION = 'position'
+ORDER = 'order'
+EVENT = 'event'
+EVENT_OR_SUBEVENT = 'event_or_subevent'
+AVAILABLE_MODELS = {
+    'OrderPosition': (ORDER_POSITION, ORDER, EVENT_OR_SUBEVENT, EVENT),
+    'Order': (ORDER, EVENT),
+}
+
+
+DataFieldInfo = namedtuple(
+    'DataFieldInfo',
+    field_names=('required_input', 'key', 'label', 'type', 'enum_opts', 'getter', 'deprecated'),
+    defaults=[False]
+)
+
+
+def get_invoice_address_or_empty(order):
+    try:
+        return order.invoice_address
+    except InvoiceAddress.DoesNotExist:
+        return InvoiceAddress()
+
+
+def get_data_fields(event, for_model=None):
+    """
+    Returns tuple of (required_input, key, label, type, enum_opts, getter)
+
+    Type is one of the Question types as defined in Question.TYPE_CHOICES.
+
+    The data type of the return value of `getter` depends on `type`:
+    - TYPE_CHOICE_MULTIPLE: list of strings
+    - TYPE_CHOICE: list, containing zero or one strings
+    - TYPE_BOOLEAN: boolean
+    - all other (including TYPE_NUMBER): string
+    """
+    name_scheme = PERSON_NAME_SCHEMES[event.settings.name_scheme]
+    name_headers = []
+    if name_scheme and len(name_scheme["fields"]) > 1:
+        for k, label, w in name_scheme["fields"]:
+            name_headers.append(label)
+
+    src_fields = (
+        [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_name",
+                _("Attendee name"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.attendee_name
+                or (position.addon_to.attendee_name if position.addon_to else None),
+            ),
+        ]
+        + [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_name_" + k,
+                _("Attendee") + ": " + label,
+                Question.TYPE_STRING,
+                None,
+                partial(
+                    lambda k, position: (
+                        position.attendee_name_parts
+                        or (position.addon_to.attendee_name_parts if position.addon_to else {})
+                        or {}
+                    ).get(k, ""),
+                    k,
+                ),
+                deprecated=len(name_scheme["fields"]) == 1,
+            )
+            for k, label, w in name_scheme["fields"]
+        ]
+        + [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_email",
+                _("Attendee email"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.attendee_email
+                or (position.addon_to.attendee_email if position.addon_to else None),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_or_order_email",
+                _("Attendee or order email"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.attendee_email
+                or (position.addon_to.attendee_email if position.addon_to else None)
+                or position.order.email,
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_company",
+                _("Attendee company"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.company or (position.addon_to.company if position.addon_to else None),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_street",
+                _("Attendee address street"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.street or (position.addon_to.street if position.addon_to else None),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_zipcode",
+                _("Attendee address ZIP code"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.zipcode or (position.addon_to.zipcode if position.addon_to else None),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_city",
+                _("Attendee address city"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.city or (position.addon_to.city if position.addon_to else None),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_country",
+                _("Attendee address country"),
+                Question.TYPE_COUNTRYCODE,
+                None,
+                lambda position: str(
+                    position.country or (position.addon_to.attendee_name if position.addon_to else "")
+                ),
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_company",
+                _("Invoice address company"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: get_invoice_address_or_empty(order).company,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_name",
+                _("Invoice address name"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: get_invoice_address_or_empty(order).name,
+            ),
+        ]
+        + [
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_name_" + k,
+                _("Invoice address") + ": " + label,
+                Question.TYPE_STRING,
+                None,
+                partial(
+                    lambda k, order: (get_invoice_address_or_empty(order).name_parts or {}).get(
+                        k, ""
+                    ),
+                    k,
+                ),
+                deprecated=len(name_scheme["fields"]) == 1,
+            )
+            for k, label, w in name_scheme["fields"]
+        ]
+        + [
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_street",
+                _("Invoice address street"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: get_invoice_address_or_empty(order).street,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_zipcode",
+                _("Invoice address ZIP code"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: get_invoice_address_or_empty(order).zipcode,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_city",
+                _("Invoice address city"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: get_invoice_address_or_empty(order).city,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_country",
+                _("Invoice address country"),
+                Question.TYPE_COUNTRYCODE,
+                None,
+                lambda order: str(get_invoice_address_or_empty(order).country),
+            ),
+            DataFieldInfo(
+                ORDER,
+                "email",
+                _("Order email"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: order.email,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "order_code",
+                _("Order code"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: order.code,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "event_order_code",
+                _("Event and order code"),
+                Question.TYPE_STRING,
+                None,
+                lambda order: order.full_code,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "order_total",
+                _("Order total"),
+                Question.TYPE_NUMBER,
+                None,
+                lambda order: str(order.total),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "product",
+                _("Product and variation name"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: str(
+                    str(position.item.internal_name or position.item.name)
+                    + ((" – " + str(position.variation.value)) if position.variation else "")
+                ),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "product_id",
+                _("Product ID"),
+                Question.TYPE_NUMBER,
+                None,
+                lambda position: str(position.item.pk),
+            ),
+            DataFieldInfo(
+                EVENT,
+                "event_slug",
+                _("Event short form"),
+                Question.TYPE_STRING,
+                None,
+                lambda event: str(event.slug),
+            ),
+            DataFieldInfo(
+                EVENT,
+                "event_name",
+                _("Event name"),
+                Question.TYPE_STRING,
+                None,
+                lambda event: str(event.name),
+            ),
+            DataFieldInfo(
+                EVENT_OR_SUBEVENT,
+                "event_date_from",
+                _("Event start date"),
+                Question.TYPE_DATETIME,
+                None,
+                lambda event_or_subevent: isoformat_or_none(event_or_subevent.date_from),
+            ),
+            DataFieldInfo(
+                EVENT_OR_SUBEVENT,
+                "event_date_to",
+                _("Event end date"),
+                Question.TYPE_DATETIME,
+                None,
+                lambda event_or_subevent: isoformat_or_none(event_or_subevent.date_to),
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "voucher_code",
+                _("Voucher code"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.voucher.code if position.voucher_id else "",
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "ticket_id",
+                _("Order code and position number"),
+                Question.TYPE_STRING,
+                None,
+                lambda position: position.code,
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "ticket_price",
+                _("Ticket price"),
+                Question.TYPE_NUMBER,
+                None,
+                lambda position: str(position.price),
+            ),
+            DataFieldInfo(
+                ORDER,
+                "order_status",
+                _("Order status"),
+                Question.TYPE_CHOICE,
+                Order.STATUS_CHOICE,
+                lambda order: [order.status],
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "ticket_status",
+                _("Ticket status"),
+                Question.TYPE_CHOICE,
+                Order.STATUS_CHOICE,
+                lambda position: [Order.STATUS_CANCELED if position.canceled else position.order.status],
+            ),
+            DataFieldInfo(
+                ORDER,
+                "order_date",
+                _("Order date and time"),
+                Question.TYPE_DATETIME,
+                None,
+                lambda order: order.datetime.isoformat(),
+            ),
+            DataFieldInfo(
+                ORDER,
+                "payment_date",
+                _("Payment date and time"),
+                Question.TYPE_DATETIME,
+                None,
+                get_payment_date,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "order_locale",
+                _("Order language code"),
+                Question.TYPE_CHOICE,
+                [(lc, lc) for lc in event.settings.locales],
+                lambda order: [order.locale],
+            ),
+            DataFieldInfo(
+                ORDER_POSITION,
+                "position_id",
+                _("Order position ID"),
+                Question.TYPE_NUMBER,
+                None,
+                lambda op: str(op.pk),
+            ),
+        ]
+        + [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "checkin_date_" + str(cl.pk),
+                _("Check-in datetime on list {}").format(cl.name),
+                Question.TYPE_DATETIME,
+                None,
+                partial(first_checkin_on_list, cl.pk),
+            )
+            for cl in event.checkin_lists.all()
+        ]
+        + [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "question_" + q.identifier,
+                _("Question: {name}").format(name=str(q.question)),
+                q.type,
+                get_enum_opts(q),
+                partial(lambda qq, position: get_answer(position, qq.identifier), q),
+            )
+            for q in event.questions.filter(~Q(type=Question.TYPE_FILE)).prefetch_related("options")
+        ]
+    )
+    if not any(field_name == "given_name" for field_name, label, weight in name_scheme["fields"]):
+        src_fields += [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_name_given_name",
+                _("Attendee") + ": " + _("Given name") + " (⚠️ auto-generated, not recommended)",
+                Question.TYPE_STRING,
+                None,
+                lambda position: split_name_on_last_space(position.attendee_name, part=0),
+                deprecated=True,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_name_given_name",
+                _("Invoice address") + ": " + _("Given name") + " (⚠️ auto-generated, not recommended)",
+                Question.TYPE_STRING,
+                None,
+                lambda order: split_name_on_last_space(get_invoice_address_or_empty(order).name, part=0),
+                deprecated=True,
+            ),
+        ]
+
+    if not any(field_name == "family_name" for field_name, label, weight in name_scheme["fields"]):
+        src_fields += [
+            DataFieldInfo(
+                ORDER_POSITION,
+                "attendee_name_family_name",
+                _("Attendee") + ": " + _("Family name") + " (⚠️ auto-generated, not recommended)",
+                Question.TYPE_STRING,
+                None,
+                lambda position: split_name_on_last_space(position.attendee_name, part=1),
+                deprecated=True,
+            ),
+            DataFieldInfo(
+                ORDER,
+                "invoice_address_name_family_name",
+                _("Invoice address") + ": " + _("Family name") + " (⚠️ auto-generated, not recommended)",
+                Question.TYPE_STRING,
+                None,
+                lambda order: split_name_on_last_space(get_invoice_address_or_empty(order).name, part=1),
+                deprecated=True,
+            ),
+        ]
+
+    if for_model:
+        available_inputs = AVAILABLE_MODELS[for_model]
+        return [
+            f for f in src_fields if f.required_input in available_inputs
+        ]
+    else:
+        return src_fields
+
+
+def get_enum_opts(q):
+    if q.type in (Question.TYPE_CHOICE, Question.TYPE_CHOICE_MULTIPLE):
+        return [(opt.identifier, opt.answer) for opt in q.options.all()]
+    else:
+        return None

src/pretix/base/datasync/utils.py

@@ -0,0 +1,122 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import json
+from typing import List, Tuple
+
+from pretix.base.datasync.datasync import SyncConfigError
+from pretix.base.models.datasync import (
+    MODE_APPEND_LIST, MODE_OVERWRITE, MODE_SET_IF_EMPTY, MODE_SET_IF_NEW,
+)
+
+
+def assign_properties(
+    new_values: List[Tuple[str, str, str]], old_values: dict, is_new, list_sep
+):
+    """
+    Generates a dictionary mapping property keys to new values, handling conditional overwrites and list updates
+    according to an update mode specified per property.
+
+    Supported update modes are:
+     - `MODE_OVERWRITE`:  Replaces the existing value with the new value.
+     - `MODE_SET_IF_NEW`: Only sets the property if `is_new` is True.
+     - `MODE_SET_IF_EMPTY`: Only sets the property if the field is empty or missing in old_values.
+     - `MODE_APPEND_LIST`: Appends the new value to the list from old_values (or the empty list if missing),
+                           using `list_sep` as a separator.
+
+    :param new_values: List of tuples, where each tuple contains (field_name, new_value, update_mode).
+    :param old_values: Dictionary, current property values in the external system.
+    :param is_new: Boolean, whether the object will be newly created in the external system.
+    :param list_sep: If string, used as a separator for MODE_APPEND_LIST. If None, native lists are used.
+    :raises SyncConfigError: If an invalid update mode is specified.
+    :returns: A dictionary containing the properties that need to be updated in the external system.
+    """
+
+    out = {}
+
+    for field_name, new_value, update_mode in new_values:
+        if update_mode == MODE_OVERWRITE:
+            out[field_name] = new_value
+            continue
+        elif update_mode == MODE_SET_IF_NEW and not is_new:
+            continue
+        if not new_value:
+            continue
+
+        current_value = old_values.get(field_name, out.get(field_name, ""))
+        if update_mode in (MODE_SET_IF_EMPTY, MODE_SET_IF_NEW):
+            if not current_value:
+                out[field_name] = new_value
+        elif update_mode == MODE_APPEND_LIST:
+            _add_to_list(out, field_name, current_value, new_value, list_sep)
+        else:
+            raise SyncConfigError(["Invalid update mode " + update_mode])
+    return out
+
+
+def _add_to_list(out, field_name, current_value, new_item, list_sep):
+    new_item = str(new_item)
+    if list_sep is not None:
+        new_item = new_item.replace(list_sep, "")
+        current_value = current_value.split(list_sep) if current_value else []
+    elif not isinstance(current_value, (list, tuple)):
+        current_value = [str(current_value)]
+    if new_item not in current_value:
+        new_list = current_value + [new_item]
+        if list_sep is not None:
+            new_list = list_sep.join(new_list)
+        out[field_name] = new_list
+
+
+def translate_property_mappings(property_mappings, checkin_list_map):
+    """
+    To properly handle copied events, users of data fields as provided by get_data_fields need to register to the
+    event_copy_data signal and translate all stored references to those fields using this method.
+
+    For example, if you store your mappings in a custom Django model with a ForeignKey to Event:
+
+    .. code-block:: python
+
+        @receiver(signal=event_copy_data, dispatch_uid="my_sync_event_copy_data")
+        def event_copy_data_receiver(sender, other, checkin_list_map, **kwargs):
+            object_mappings = other.my_object_mappings.all()
+            object_mapping_map = {}
+            for om in object_mappings:
+                om = copy.copy(om)
+                object_mapping_map[om.pk] = om
+                om.pk = None
+                om.event = sender
+                om.property_mappings = translate_property_mappings(om.property_mappings, checkin_list_map)
+                om.save()
+
+    """
+    mappings = json.loads(property_mappings)
+
+    for mapping in mappings:
+        if mapping["pretix_field"].startswith("checkin_date_"):
+            old_id = int(mapping["pretix_field"][len("checkin_date_"):])
+            if old_id not in checkin_list_map:
+                # old_id might not be in checkin_list_map, because copying of an event series only copies check-in
+                # lists covering the whole series, not individual dates.
+                mapping["pretix_field"] = "_invalid_" + mapping["pretix_field"]
+            else:
+                mapping["pretix_field"] = "checkin_date_%d" % checkin_list_map[old_id].pk
+    return json.dumps(mappings)

src/pretix/base/migrations/0284_ordersyncresult_ordersyncqueue.py

@@ -0,0 +1,54 @@
+# Generated by Django 4.2.21 on 2025-06-27 13:32
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0283_taxrule_default_taxrule_backfill'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='OrderSyncResult',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False)),
+                ('sync_provider', models.CharField(max_length=128)),
+                ('mapping_id', models.IntegerField()),
+                ('external_object_type', models.CharField(max_length=128)),
+                ('external_id_field', models.CharField(max_length=128)),
+                ('id_value', models.CharField(max_length=128)),
+                ('external_link_href', models.CharField(max_length=255, null=True)),
+                ('external_link_display_name', models.CharField(max_length=255, null=True)),
+                ('transmitted', models.DateTimeField(auto_now_add=True)),
+                ('sync_info', models.JSONField()),
+                ('order', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='sync_results', to='pretixbase.order')),
+                ('order_position', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='sync_results', to='pretixbase.orderposition')),
+            ],
+            options={
+                'indexes': [models.Index(fields=['order', 'sync_provider'], name='pretixbase__order_i_3e3c84_idx')],
+            },
+        ),
+        migrations.CreateModel(
+            name='OrderSyncQueue',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False)),
+                ('sync_provider', models.CharField(max_length=128)),
+                ('triggered_by', models.CharField(max_length=128)),
+                ('triggered', models.DateTimeField(auto_now_add=True)),
+                ('failed_attempts', models.PositiveIntegerField(default=0)),
+                ('not_before', models.DateTimeField(db_index=True)),
+                ('need_manual_retry', models.CharField(null=True, max_length=20)),
+                ('in_flight', models.BooleanField(default=False)),
+                ('in_flight_since', models.DateTimeField(blank=True, null=True)),
+                ('event', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='queued_sync_jobs', to='pretixbase.event')),
+                ('order', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='queued_sync_jobs', to='pretixbase.order')),
+            ],
+            options={
+                'ordering': ('triggered',),
+                'unique_together': {('order', 'sync_provider', 'in_flight')},
+            },
+        ),
+    ]

src/pretix/base/models/datasync.py

@@ -0,0 +1,149 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+import logging
+from functools import cached_property
+
+from django.db import IntegrityError, models
+from django.utils.translation import gettext as _
+
+from pretix.base.models import Event, Order, OrderPosition
+
+logger = logging.getLogger(__name__)
+
+
+MODE_OVERWRITE = "overwrite"
+MODE_SET_IF_NEW = "if_new"
+MODE_SET_IF_EMPTY = "if_empty"
+MODE_APPEND_LIST = "append"
+
+
+class OrderSyncQueue(models.Model):
+    order = models.ForeignKey(
+        Order, on_delete=models.CASCADE, related_name="queued_sync_jobs"
+    )
+    event = models.ForeignKey(
+        Event, on_delete=models.CASCADE, related_name="queued_sync_jobs"
+    )
+    sync_provider = models.CharField(blank=False, null=False, max_length=128)
+    triggered_by = models.CharField(blank=False, null=False, max_length=128)
+    triggered = models.DateTimeField(blank=False, null=False, auto_now_add=True)
+    failed_attempts = models.PositiveIntegerField(default=0)
+    not_before = models.DateTimeField(blank=False, null=False, db_index=True)
+    need_manual_retry = models.CharField(blank=True, null=True, max_length=20, choices=[
+        ('exceeded', _('Temporary error, auto-retry limit exceeded')),
+        ('permanent', _('Provider reported a permanent error')),
+        ('config', _('Misconfiguration, please check provider settings')),
+        ('internal', _('System error, needs manual intervention')),
+        ('timeout', _('System error, needs manual intervention')),
+    ])
+    in_flight = models.BooleanField(default=False)
+    in_flight_since = models.DateTimeField(blank=True, null=True)
+
+    class Meta:
+        unique_together = (("order", "sync_provider", "in_flight"),)
+        ordering = ("triggered",)
+
+    @cached_property
+    def _provider_class_info(self):
+        from pretix.base.datasync.datasync import datasync_providers
+        return datasync_providers.get(identifier=self.sync_provider)
+
+    @property
+    def provider_class(self):
+        return self._provider_class_info[0]
+
+    @property
+    def provider_display_name(self):
+        return self.provider_class.display_name
+
+    @property
+    def is_provider_active(self):
+        return self._provider_class_info[1]
+
+    @property
+    def max_retry_attempts(self):
+        return self.provider_class.max_attempts
+
+    def set_sync_error(self, failure_mode, messages, full_message):
+        logger.exception(
+            f"Could not sync order {self.order.code} to {type(self).__name__} ({failure_mode})"
+        )
+        self.order.log_action(f"pretix.event.order.data_sync.failed.{failure_mode}", {
+            "provider": self.sync_provider,
+            "error": messages,
+            "full_message": full_message,
+        })
+        self.need_manual_retry = failure_mode
+        self.clear_in_flight()
+
+    def clear_in_flight(self):
+        self.in_flight = False
+        self.in_flight_since = None
+        try:
+            self.save()
+        except IntegrityError:
+            # if setting in_flight=False fails due to UNIQUE constraint, just delete the current instance
+            self.delete()
+
+
+class OrderSyncResult(models.Model):
+    order = models.ForeignKey(
+        Order, on_delete=models.CASCADE, related_name="sync_results"
+    )
+    sync_provider = models.CharField(blank=False, null=False, max_length=128)
+    order_position = models.ForeignKey(
+        OrderPosition, on_delete=models.CASCADE, related_name="sync_results", blank=True, null=True,
+    )
+    mapping_id = models.IntegerField(blank=False, null=False)
+    external_object_type = models.CharField(blank=False, null=False, max_length=128)
+    external_id_field = models.CharField(blank=False, null=False, max_length=128)
+    id_value = models.CharField(blank=False, null=False, max_length=128)
+    external_link_href = models.CharField(blank=True, null=True, max_length=255)
+    external_link_display_name = models.CharField(blank=True, null=True, max_length=255)
+    transmitted = models.DateTimeField(blank=False, null=False, auto_now_add=True)
+    sync_info = models.JSONField()
+
+    class Meta:
+        indexes = [
+            models.Index(fields=("order", "sync_provider")),
+        ]
+
+    def external_link_html(self):
+        if not self.external_link_display_name:
+            return None
+
+        from pretix.base.datasync.datasync import datasync_providers
+        prov, meta = datasync_providers.get(identifier=self.sync_provider)
+        if prov:
+            return prov.get_external_link_html(self.order.event, self.external_link_href, self.external_link_display_name)
+
+    def to_result_dict(self):
+        return {
+            "position": self.order_position_id,
+            "object_type": self.external_object_type,
+            "external_id_field": self.external_id_field,
+            "id_value": self.id_value,
+            "external_link_href": self.external_link_href,
+            "external_link_display_name": self.external_link_display_name,
+            **self.sync_info,
+        }

src/pretix/base/services/datasync.py

@@ -0,0 +1,83 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+import logging
+from datetime import timedelta
+from itertools import groupby
+
+from django.db.models import F, Window
+from django.db.models.functions import RowNumber
+from django.dispatch import receiver
+from django.utils.timezone import now
+from django_scopes import scope, scopes_disabled
+
+from pretix.base.datasync.datasync import datasync_providers
+from pretix.base.models.datasync import OrderSyncQueue
+from pretix.base.signals import periodic_task
+from pretix.celery_app import app
+
+logger = logging.getLogger(__name__)
+
+
+@receiver(periodic_task, dispatch_uid="data_sync_periodic_sync_all")
+def periodic_sync_all(sender, **kwargs):
+    sync_all.apply_async()
+
+
+@receiver(periodic_task, dispatch_uid="data_sync_periodic_reset_in_flight")
+def periodic_reset_in_flight(sender, **kwargs):
+    for sq in OrderSyncQueue.objects.filter(
+        in_flight=True,
+        in_flight_since__lt=now() - timedelta(minutes=20),
+    ):
+        sq.set_sync_error('timeout', [], 'Timeout')
+
+
+@app.task()
+def sync_all():
+    with scopes_disabled():
+        queue = (
+            OrderSyncQueue.objects
+            .filter(
+                in_flight=False,
+                not_before__lt=now(),
+                need_manual_retry__isnull=True,
+            )
+            .order_by(Window(
+                expression=RowNumber(),
+                partition_by=[F("event_id")],
+                order_by="not_before",
+            ))
+            .prefetch_related("event")
+            [:1000]
+        )
+        grouped = groupby(sorted(queue, key=lambda q: (q.sync_provider, q.event.pk)), lambda q: (q.sync_provider, q.event))
+        for (target, event), queued_orders in grouped:
+            target_cls, meta = datasync_providers.get(identifier=target, active_in=event)
+
+            if not target_cls:
+                # sync plugin not found (plugin deactivated or uninstalled) -> drop outstanding jobs
+                OrderSyncQueue.objects.filter(pk__in=[sq.pk for sq in queued_orders]).delete()
+
+            with scope(organizer=event.organizer):
+                with target_cls(event=event) as p:
+                    p.sync_queued_orders(queued_orders)

src/pretix/base/signals.py

@@ -257,8 +257,14 @@ class Registry:
                      When a new entry is registered, all accessor functions are called with the new entry as parameter.
                      Their return value is stored as the metadata value for that key.
         """
-        self.registered_entries = dict()
         self.keys = keys
+        self.clear()
+
+    def clear(self):
+        """
+        Removes all entries from the registry.
+        """
+        self.registered_entries = dict()
         self.by_key = {key: {} for key in self.keys.keys()}
 
     def register(self, *objs):
@@ -333,6 +339,23 @@ class EventPluginRegistry(Registry):
     def __init__(self, keys):
         super().__init__({"plugin": lambda o: get_defining_app(o), **keys})
 
+    def filter(self, active_in=None, **kwargs):
+        result = super().filter(**kwargs)
+        if active_in is not None:
+            result = (
+                (entry, meta)
+                for entry, meta in result
+                if is_app_active(active_in, meta['plugin'])
+            )
+        return result
+
+    def get(self, active_in=None, **kwargs):
+        item, meta = super().get(**kwargs)
+        if meta and active_in is not None:
+            if not is_app_active(active_in, meta['plugin']):
+                return None, None
+        return item, meta
+
 
 event_live_issues = EventPluginSignal()
 """

src/pretix/control/apps.py

@@ -42,3 +42,4 @@ class PretixControlConfig(AppConfig):
     def ready(self):
         from .views import dashboards  # noqa
         from . import logdisplay  # noqa
+        from .views import datasync  # noqa

src/pretix/control/forms/mapping.py

@@ -0,0 +1,127 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import json
+
+from django import forms
+from django.forms import formset_factory
+from django.utils.translation import gettext_lazy as _
+
+from pretix.base.models import Question
+from pretix.base.models.datasync import (
+    MODE_APPEND_LIST, MODE_OVERWRITE, MODE_SET_IF_EMPTY, MODE_SET_IF_NEW,
+)
+
+
+class PropertyMappingForm(forms.Form):
+    pretix_field = forms.CharField()
+    external_field = forms.CharField()
+    value_map = forms.CharField(required=False)
+    overwrite = forms.ChoiceField(
+        choices=[
+            (MODE_OVERWRITE, _("Overwrite")),
+            (MODE_SET_IF_NEW, _("Fill if new")),
+            (MODE_SET_IF_EMPTY, _("Fill if empty")),
+            (MODE_APPEND_LIST, _("Add to list")),
+        ]
+    )
+
+    def __init__(self, pretix_fields, external_fields_id, available_modes, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields["pretix_field"] = forms.ChoiceField(
+            label=_("pretix field"),
+            choices=pretix_fields_choices(pretix_fields, kwargs.get("initial", {}).get("pretix_field")),
+            required=False,
+        )
+        if external_fields_id:
+            self.fields["external_field"] = forms.ChoiceField(
+                widget=forms.Select(
+                    attrs={
+                        "data-model-select2": "json_script",
+                        "data-select2-src": "#" + external_fields_id,
+                    },
+                ),
+            )
+            self.fields["external_field"].choices = [
+                (self["external_field"].value(), self["external_field"].value()),
+            ]
+        self.fields["overwrite"].choices = [
+            (key, label) for (key, label) in self.fields["overwrite"].choices if key in available_modes
+        ]
+
+
+class PropertyMappingFormSet(formset_factory(
+    PropertyMappingForm,
+    can_order=True,
+    can_delete=True,
+    extra=0,
+)):
+    template_name = "pretixcontrol/datasync/property_mappings_formset.html"
+
+    def __init__(self, pretix_fields, external_fields, available_modes, prefix, *args, initial_json=None, **kwargs):
+        if initial_json:
+            kwargs["initial"] = json.loads(initial_json)
+        super().__init__(
+            form_kwargs={
+                "pretix_fields": pretix_fields,
+                "external_fields_id": prefix + "external-fields" if external_fields else None,
+                "available_modes": available_modes,
+            },
+            prefix=prefix,
+            *args, **kwargs)
+        self.external_fields = external_fields
+
+    def get_context(self):
+        ctx = super().get_context()
+        ctx["external_fields"] = self.external_fields
+        ctx["external_fields_id"] = self.prefix + "external-fields"
+        return ctx
+
+    def to_property_mappings_json(self):
+        """
+        Returns a property mapping configuration as a JSON-serialized list of dictionaries.
+
+        Each entry specifies how to transfer data from one pretix field to one field in the external system:
+
+          - `pretix_field`: Name of a pretix data source field as declared in `pretix.base.datasync.sourcefields.get_data_fields`.
+          - `external_field`: Name of the target field in the external system. Implementation-defined by the sync provider.
+          - `value_map`: Dictionary mapping pretix value to external value. Only used for enumeration-type fields.
+          - `overwrite`: Mode of operation if the object already exists in the target system.
+
+            - `MODE_OVERWRITE` (`"overwrite"`) to always overwrite existing value.
+            - `MODE_SET_IF_NEW` (`"if_new"`) to only set the value if object does not exist in target system yet.
+            - `MODE_SET_IF_EMPTY` (`"if_empty"`) to only set the value if object does not exist in target system,
+              or the field is currently empty in target system.
+            - `MODE_APPEND_LIST` (`"append"`) if the field is an array or a multi-select: add the value to the list.
+        """
+        mappings = [f.cleaned_data for f in self.ordered_forms]
+        return json.dumps(mappings)
+
+
+QUESTION_TYPE_LABELS = dict(Question.TYPE_CHOICES)
+
+
+def pretix_fields_choices(pretix_fields, initial_choice):
+    return [
+        (f.key, f.label + " [" + QUESTION_TYPE_LABELS[f.type] + "]")
+        for f in pretix_fields
+        if not f.deprecated or f.key == initial_choice
+    ]

src/pretix/control/logdisplay.py

@@ -43,9 +43,11 @@ from django.dispatch import receiver
 from django.urls import reverse
 from django.utils.formats import date_format
 from django.utils.html import escape, format_html
+from django.utils.safestring import mark_safe
 from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from i18nfield.strings import LazyI18nString
 
+from pretix.base.datasync.datasync import datasync_providers
 from pretix.base.logentrytypes import (
     DiscountLogEntryType, EventLogEntryType, ItemCategoryLogEntryType,
     ItemLogEntryType, LogEntryType, OrderLogEntryType, QuestionLogEntryType,
@@ -421,6 +423,51 @@ class OrderPrintLogEntryType(OrderLogEntryType):
         )
 
 
+class OrderDataSyncLogEntryType(OrderLogEntryType):
+    def display(self, logentry, data):
+        try:
+            from pretix.base.datasync.datasync import datasync_providers
+            provider_class, meta = datasync_providers.get(identifier=data['provider'])
+            data['provider_display_name'] = provider_class.display_name
+        except (KeyError, AttributeError):
+            data['provider_display_name'] = data.get('provider')
+        return super().display(logentry, data)
+
+
+@log_entry_types.new_from_dict({
+    "pretix.event.order.data_sync.success": _("Data successfully transferred to {provider_display_name}."),
+})
+class OrderDataSyncSuccessLogEntryType(OrderDataSyncLogEntryType):
+    def display(self, logentry, data):
+        links = []
+        if data.get('provider') and data.get('objects'):
+            prov, meta = datasync_providers.get(identifier=data['provider'])
+            if prov:
+                for objs in data['objects'].values():
+                    links.append(", ".join(
+                        prov.get_external_link_html(logentry.event, obj['external_link_href'], obj['external_link_display_name'])
+                        for obj in objs
+                        if obj and 'external_link_href' in obj and 'external_link_display_name' in obj
+                    ))
+
+        return mark_safe(escape(super().display(logentry, data)) + "".join("<p>" + link + "</p>" for link in links))
+
+
+@log_entry_types.new_from_dict({
+    "pretix.event.order.data_sync.failed.config": _("Transferring data to {provider_display_name} failed due to invalid configuration:"),
+    "pretix.event.order.data_sync.failed.exceeded": _("Maximum number of retries exceeded while transferring data to {provider_display_name}:"),
+    "pretix.event.order.data_sync.failed.permanent": _("Error while transferring data to {provider_display_name}:"),
+    "pretix.event.order.data_sync.failed.internal": _("Internal error while transferring data to {provider_display_name}."),
+    "pretix.event.order.data_sync.failed.timeout": _("Internal error while transferring data to {provider_display_name}."),
+})
+class OrderDataSyncErrorLogEntryType(OrderDataSyncLogEntryType):
+    def display(self, logentry, data):
+        errmes = data["error"]
+        if not isinstance(errmes, list):
+            errmes = [errmes]
+        return mark_safe(escape(super().display(logentry, data)) + "".join("<p>" + escape(msg) + "</p>" for msg in errmes))
+
+
 @receiver(signal=logentry_display, dispatch_uid="pretixcontrol_logentry_display")
 def pretixcontrol_logentry_display(sender: Event, logentry: LogEntry, **kwargs):
 

src/pretix/control/navigation.py

@@ -451,6 +451,11 @@ def get_global_navigation(request):
                     'url': reverse('control:global.sysreport'),
                     'active': (url.url_name == 'global.sysreport'),
                 },
+                {
+                    'label': _('Data sync problems'),
+                    'url': reverse('control:global.datasync.failedjobs'),
+                    'active': (url.url_name == 'global.datasync.failedjobs'),
+                },
             ]
         })
 
@@ -655,6 +660,18 @@ def get_organizer_navigation(request):
         'icon': 'download',
     })
 
+    if 'can_change_organizer_settings' in request.orgapermset:
+        merge_in(nav, [{
+            'parent': reverse('control:organizer.export', kwargs={
+                'organizer': request.organizer.slug,
+            }),
+            'label': _('Data sync problems'),
+            'url': reverse('control:organizer.datasync.failedjobs', kwargs={
+                'organizer': request.organizer.slug,
+            }),
+            'active': (url.url_name == 'organizer.datasync.failedjobs'),
+        }])
+
     merge_in(nav, sorted(
         sum((list(a[1]) for a in nav_organizer.send(request.organizer, request=request, organizer=request.organizer)),
             []),

src/pretix/control/templates/pretixcontrol/datasync/control_order_info.html

@@ -0,0 +1,74 @@
+{% load i18n %}
+{% load eventurl %}
+{% load bootstrap3 %}
+{% load escapejson %}
+<div class="panel panel-default">
+    <div class="panel-heading">
+        <h3 class="panel-title">
+            {% trans "Data transfer to external systems" %}
+        </h3>
+    </div>
+    <ul class="list-group">
+        {% for identifier, display_name, pending, objects in providers %}
+            <li class="list-group-item">
+                <form action="{% url "control:event.order.sync_job" organizer=event.organizer.slug event=event.slug code=order.code provider=identifier %}" method="post" class="form-inline pull-right">
+                    {% csrf_token %}
+                    {% if pending %}
+                        {% if pending.not_before > now or pending.need_manual_retry %}
+                            <button type="submit" name="run_job_now" value="{{ pending.pk }}" class="btn btn-default"><i class="fa fa-refresh"></i> {% trans "Retry now" %}</button>
+                        {% endif %}
+                        <button type="submit" name="cancel_job" value="{{ pending.pk }}" class="btn btn-danger"><i class="fa fa-times"></i> {% trans "Cancel" %}</button>
+                    {% else %}
+                        <button type="submit" class="btn btn-default"><i class="fa fa-refresh"></i> {% trans "Sync now" %}</button>
+                        <input type="hidden" name="queue_sync" value="true">
+                    {% endif %}
+                </form>
+                <p><b>{{ display_name }}</b></p>
+                {% if pending %}
+                    <p>
+                        {% if pending.need_manual_retry %}
+                            <i class="fa fa-warning"></i>
+                            {% trans "Error" %}: {{ pending.get_need_manual_retry_display }}
+                        {% elif pending.failed_attempts %}
+                            <i class="fa fa-warning"></i>
+                            {% blocktrans trimmed with num=pending.failed_attempts max=pending.max_retry_attempts %}
+                            Error. Retry {{ num }} of {{ max }}.
+                            {% endblocktrans %}
+                            {% if pending.not_before %}
+                                {% blocktrans trimmed with datetime=pending.not_before|date:"SHORT_DATETIME_FORMAT" %}
+                                Waiting until {{ datetime }}
+                                {% endblocktrans %}
+                            {% endif %}
+                        {% elif pending.not_before > now %}
+                            {% blocktrans trimmed with datetime=pending.not_before|date:"SHORT_DATETIME_FORMAT" %}
+                            Waiting until {{ datetime }}
+                            {% endblocktrans %}
+                        {% else %}
+                            <i class="fa fa-hourglass"></i> {% trans "Pending" %}
+                        {% endif %}
+                        <span class="text-muted">({% blocktrans trimmed with datetime=pending.triggered|date:"SHORT_DATETIME_FORMAT" %}triggered at {{ datetime }}
+                        {% endblocktrans %})</span>
+                        <!-- {{ pending.triggered_by }} / {{ pending.triggered }} -->
+                    </p>
+                {% endif %}
+
+                <ul>
+                    {% for obj in objects %}
+                        <li>
+                            {% if obj.external_link_html %}
+                                {{ obj.external_link_html }}
+                            {% else %}
+                                {{ obj.external_object_type }}
+                                {% trans "identified by" %} {{ obj.external_id_field }}
+                                <em>{{ obj.id_value }}</em>
+                            {% endif %}
+                            &nbsp; <time class="text-muted" datetime="{{ obj.transmitted.isoformat }}">{{ obj.transmitted|date:"SHORT_DATETIME_FORMAT" }}</time>
+                        </li>
+                    {% empty %}
+                        <li>{% trans "No data transmitted." %}</li>
+                    {% endfor %}
+                </ul>
+            </li>
+        {% endfor %}
+    </ul>
+</div>

src/pretix/control/templates/pretixcontrol/datasync/failed_jobs.html

@@ -0,0 +1,86 @@
+{% extends "pretixcontrol/event/base.html" %}
+{% load i18n %}
+
+{% block content %}
+    <h2>{% trans "Sync problems" %}</h2>
+    <p>
+        {% blocktrans trimmed %}
+            On this page, we provide a list of orders where data synchronisation to an external system has failed.
+            You can start another attempt to sync them manually.
+        {% endblocktrans %}
+    </p>
+    <form method="post">
+        {% csrf_token %}
+        <table class="table table-hover">
+            <thead>
+                <tr>
+                    <th>
+                        {% if queue_items %}
+                            <label aria-label="{% trans "select all rows for batch-operation" %}"
+                               class="batch-select-label"><input type="checkbox" data-toggle-table/></label>
+                        {% endif %}
+                    </th>
+                    <th>{% trans "Order" %}</th>
+                    <th>{% trans "Sync provider" %}</th>
+                    <th>{% trans "Date" %}</th>
+                    <th>{% trans "Failure mode" %}</th>
+                    {% if staff_session %}
+                        <th>in_flight</th><th>retry</th>
+                    {% endif %}
+                </tr>
+            </thead>
+            <tbody>
+                {% for item in queue_items %}
+                    <tr>
+                        <td><input type="checkbox" name="idlist" value="{{ item.pk }}"></td>
+                        <td>
+                            {% if staff_session %}{{ item.order.event.organizer.slug }} -{% endif %}
+                            <a href="{% url "control:event.order" event=item.order.event.slug organizer=item.order.event.organizer.slug code=item.order.code %}">
+                                {{ item.order.full_code }}
+                            </a>
+                        </td>
+                        <td>{{ item.provider_display_name }}</td>
+                        <td>
+                            {{ item.triggered }}
+                            {% if staff_session %}({{ item.triggered_by }}){% endif %}
+                        </td>
+                        <td>
+                            {% if item.need_manual_retry %}
+                                {{ item.get_need_manual_retry_display }}
+                            {% else %}
+                                {% blocktrans trimmed with datetime=item.not_before|date:"SHORT_DATETIME_FORMAT" %}
+                                Temporary error, will retry after {{ datetime }}
+                                {% endblocktrans %}
+                            {% endif %}
+                            {% if staff_session %}({{ item.need_manual_retry }}){% endif %}
+                        </td>
+                        {% if staff_session %}
+                            <td>{{ item.in_flight }} ({{ item.in_flight_since }})</td><td>{{ item.failed_attempts }} / {{ item.max_retry_attempts }} ({{ item.not_before }})</td>
+                        {% endif %}
+                    </tr>
+                {% empty %}
+                    <tr>
+                        <td colspan="5" class="text-center">{% trans "No problems." %}</td>
+                        {% if staff_session %}
+                            <td></td><td></td>
+                        {% endif %}
+                    </tr>
+                {% endfor %}
+            </tbody>
+        {% if queue_items %}
+            <tfoot>
+                <tr>
+                    <td colspan="5">
+                        <button type="submit" name="action" value="retry" class="btn btn-primary"><i class="fa fa-refresh"></i> {% trans "Retry selected" %}</button>
+                        <button type="submit" name="action" value="cancel" class="btn btn-danger"><i class="fa fa-times"></i> {% trans "Cancel selected" %}</button>
+                    </td>
+                    {% if staff_session %}
+                        <td></td><td></td>
+                    {% endif %}
+                </tr>
+            </tfoot>
+        {% endif %}
+        </table>
+    </form>
+    {% include "pretixcontrol/pagination.html" %}
+{% endblock %}

src/pretix/control/templates/pretixcontrol/datasync/property_mappings_formset.html

@@ -0,0 +1,81 @@
+{% load i18n %}
+{% load bootstrap3 %}
+{% load escapejson %}
+{% load formset_tags %}
+<div class="formset" data-formset data-formset-prefix="{{ formset.prefix }}">
+    {{ formset.management_form }}
+    {% bootstrap_formset_errors formset %}
+    <div data-formset-body>
+        {% for f in formset %}
+            {% bootstrap_form_errors f %}
+            <div class="row formset-row" data-formset-form>
+                <div class="sr-only">
+                    {{ f.id }}
+                    {% bootstrap_field f.DELETE form_group_class="" layout="inline" %}
+                    {% bootstrap_field f.ORDER form_group_class="" layout="inline" %}
+                </div>
+                <div class="col-md-4">
+                    {% bootstrap_field f.pretix_field layout='inline' form_group_class="" %}
+                </div>
+                <div class="col-md-4">
+                    {% bootstrap_field f.external_field layout='inline' form_group_class="" %}
+                </div>
+                <div class="col-md-2">
+                    {% bootstrap_field f.overwrite layout='inline' form_group_class="" %}
+                </div>
+                {{ f.value_map.as_hidden }}
+                <div class="col-md-2 text-right flip">
+                    <i class="fa fa-warning hidden" data-toggle="tooltip" title=""></i>
+
+                    <button type="button" class="btn btn-default hidden" data-edit-value-map data-toggle="modal"
+                            data-target="#editValueMapModal" title="{% trans "Edit value mapping" %}">
+                        <i class="fa fa-edit"></i></button>
+                    <button type="button" class="btn btn-default" data-formset-move-up-button>
+                        <i class="fa fa-arrow-up"></i></button>
+                    <button type="button" class="btn btn-default" data-formset-move-down-button>
+                        <i class="fa fa-arrow-down"></i></button>
+                    <button type="button" class="btn btn-danger" data-formset-delete-button>
+                        <i class="fa fa-trash"></i></button>
+                </div>
+            </div>
+        {% endfor %}
+    </div>
+    <script type="form-template" data-formset-empty-form>
+        {% escapescript %}
+            <div class="row formset-row" data-formset-form>
+                <div class="sr-only">
+                    {% bootstrap_field formset.empty_form.DELETE form_group_class="" layout="inline" %}
+                </div>
+                <div class="col-md-4">
+                    {% bootstrap_field formset.empty_form.pretix_field layout='inline' form_group_class="" %}
+                </div>
+                <div class="col-md-4">
+                    {% bootstrap_field formset.empty_form.external_field layout='inline' form_group_class="" %}
+                </div>
+                <div class="col-md-2">
+                    {% bootstrap_field formset.empty_form.overwrite layout='inline' form_group_class="" %}
+                </div>
+                {{ f.value_map.as_hidden }}
+                <div class="col-md-2 text-right flip">
+                    <i class="fa fa-warning hidden" data-toggle="tooltip" title=""></i>
+                    <button type="button" class="btn btn-default hidden" data-edit-value-map data-toggle="modal"
+                            data-target="#editValueMapModal" title="{% trans "Edit value mapping" %}">
+                        <i class="fa fa-edit"></i></button>
+                    <button type="button" class="btn btn-default" data-formset-move-up-button>
+                        <i class="fa fa-arrow-up"></i></button>
+                    <button type="button" class="btn btn-default" data-formset-move-down-button>
+                        <i class="fa fa-arrow-down"></i></button>
+                    <button type="button" class="btn btn-danger" data-formset-delete-button>
+                        <i class="fa fa-trash"></i></button>
+                </div>
+            </div>
+        {% endescapescript %}
+    </script>
+    <p>
+        <button type="button" class="btn btn-default" data-formset-add>
+            <i class="fa fa-plus"></i> {% trans "Add property" %}</button>
+    </p>
+</div>
+{% if external_fields %}
+    {{ external_fields|json_script:external_fields_id }}
+{% endif %}

src/pretix/control/templates/pretixcontrol/event/index.html

@@ -79,6 +79,15 @@
                     class="btn btn-primary">{% trans "Show affected orders" %}</a>
         </div>
     {% endif %}
+    {% if has_sync_problems %}
+        <div class="alert alert-warning">
+            {% blocktrans trimmed %}
+                Orders in this event could not be <strong>synced to an external system</strong> as configured.
+            {% endblocktrans %}
+            <a href="{% url "control:event.datasync.failedjobs" event=request.event.slug organizer=request.event.organizer.slug %}"
+                    class="btn btn-primary">{% trans "Show sync problems" %}</a>
+        </div>
+    {% endif %}
     {% eventsignal request.event "pretix.control.signals.event_dashboard_top" request=request %}
 
     {% if request.event.has_subevents %}

src/pretix/control/urls.py

@@ -37,9 +37,9 @@ from django.urls import include, re_path
 from django.views.generic.base import RedirectView
 
 from pretix.control.views import (
-    auth, checkin, dashboards, discounts, event, geo, global_settings, item,
+    auth, checkin, dashboards, datasync, discounts, event, geo,
-    main, modelimport, oauth, orders, organizer, pdf, search, shredder,
+    global_settings, item, main, modelimport, oauth, orders, organizer, pdf,
-    subevents, typeahead, user, users, vouchers, waitinglist,
+    search, shredder, subevents, typeahead, user, users, vouchers, waitinglist,
 )
 
 urlpatterns = [
@@ -58,6 +58,7 @@ urlpatterns = [
     re_path(r'^global/license/$', global_settings.LicenseCheckView.as_view(), name='global.license'),
     re_path(r'^global/sysreport/$', global_settings.SysReportView.as_view(), name='global.sysreport'),
     re_path(r'^global/message/$', global_settings.MessageView.as_view(), name='global.message'),
+    re_path(r'^global/datasync/failedjobs/$', datasync.GlobalFailedSyncJobsView.as_view(), name='global.datasync.failedjobs'),
     re_path(r'^logdetail/$', global_settings.LogDetailView.as_view(), name='global.logdetail'),
     re_path(r'^logdetail/payment/$', global_settings.PaymentDetailView.as_view(), name='global.paymentdetail'),
     re_path(r'^logdetail/refund/$', global_settings.RefundDetailView.as_view(), name='global.refunddetail'),
@@ -248,6 +249,7 @@ urlpatterns = [
     re_path(r'^organizer/(?P<organizer>[^/]+)/export/(?P<pk>[^/]+)/delete$', organizer.DeleteScheduledExportView.as_view(),
             name='organizer.export.scheduled.delete'),
     re_path(r'^organizer/(?P<organizer>[^/]+)/ticket_select2$', typeahead.ticket_select2, name='organizer.ticket_select2'),
+    re_path(r'^organizer/(?P<organizer>[^/]+)/datasync/failedjobs/$', datasync.OrganizerFailedSyncJobsView.as_view(), name='organizer.datasync.failedjobs'),
     re_path(r'^nav/typeahead/$', typeahead.nav_context_list, name='nav.typeahead'),
     re_path(r'^events/$', main.EventList.as_view(), name='events'),
     re_path(r'^events/add$', main.EventWizard.as_view(), name='events.add'),
@@ -428,6 +430,8 @@ urlpatterns = [
         re_path(r'^orders/(?P<code>[0-9A-Z]+)/cancellationrequests/(?P<req>\d+)/delete$',
                 orders.OrderCancellationRequestDelete.as_view(),
                 name='event.order.cancellationrequests.delete'),
+        re_path(r'^orders/(?P<code>[0-9A-Z]+)/sync_job/(?P<provider>[^/]+)/$', datasync.ControlSyncJob.as_view(),
+                name='event.order.sync_job'),
         re_path(r'^orders/(?P<code>[0-9A-Z]+)/transactions/$', orders.OrderTransactions.as_view(), name='event.order.transactions'),
         re_path(r'^orders/(?P<code>[0-9A-Z]+)/$', orders.OrderDetail.as_view(), name='event.order'),
         re_path(r'^invoice/(?P<invoice>[^/]+)$', orders.InvoiceDownload.as_view(),
@@ -474,6 +478,7 @@ urlpatterns = [
                 name='event.orders.checkinlists.edit'),
         re_path(r'^checkinlists/(?P<list>\d+)/delete$', checkin.CheckinListDelete.as_view(),
                 name='event.orders.checkinlists.delete'),
+        re_path(r'^datasync/failedjobs/$', datasync.EventFailedSyncJobsView.as_view(), name='event.datasync.failedjobs'),
     ])),
     re_path(r'^event/(?P<organizer>[^/]+)/$', RedirectView.as_view(pattern_name='control:organizer'), name='event.organizerredirect'),
 ]

src/pretix/control/views/dashboards.py

@@ -383,6 +383,10 @@ def event_index(request, organizer, event):
     ctx['has_cancellation_requests'] = can_view_orders and CancellationRequest.objects.filter(
         order__event=request.event
     ).exists()
+    ctx['has_sync_problems'] = can_change_event_settings and request.event.queued_sync_jobs.filter(
+        Q(need_manual_retry__isnull=False)
+        | Q(failed_attempts__gt=0)
+    ).exists()
 
     ctx['timeline'] = [
         {

src/pretix/control/views/datasync.py

@@ -0,0 +1,150 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+from itertools import groupby
+
+from django.contrib import messages
+from django.db.models import Q
+from django.dispatch import receiver
+from django.http import HttpResponseNotAllowed
+from django.shortcuts import redirect
+from django.template.loader import get_template
+from django.utils.timezone import now
+from django.utils.translation import gettext_lazy as _
+from django.views.generic import ListView
+
+from pretix.base.datasync.datasync import datasync_providers
+from pretix.base.models import Event, Order
+from pretix.base.models.datasync import OrderSyncQueue
+from pretix.control.permissions import (
+    AdministratorPermissionRequiredMixin, EventPermissionRequiredMixin,
+    OrganizerPermissionRequiredMixin,
+)
+from pretix.control.signals import order_info
+from pretix.control.views.orders import OrderView
+
+
+@receiver(order_info, dispatch_uid="datasync_control_order_info")
+def on_control_order_info(sender: Event, request, order: Order, **kwargs):
+    providers = [provider for provider, meta in datasync_providers.filter(active_in=sender)]
+    if not providers:
+        return ""
+
+    queued = {p.sync_provider: p for p in order.queued_sync_jobs.all()}
+    objects = {
+        provider: list(objects)
+        for (provider, objects)
+        in groupby(order.sync_results.order_by('sync_provider').all(), key=lambda o: o.sync_provider)
+    }
+    providers = [(provider.identifier, provider.display_name, queued.get(provider.identifier), objects.get(provider.identifier)) for provider in providers]
+
+    template = get_template("pretixcontrol/datasync/control_order_info.html")
+    ctx = {
+        "order": order,
+        "request": request,
+        "event": sender,
+        "providers": providers,
+        "now": now(),
+    }
+    return template.render(ctx, request=request)
+
+
+class ControlSyncJob(OrderView):
+    permission = 'can_change_orders'
+
+    def post(self, request, provider, *args, **kwargs):
+        prov, meta = datasync_providers.get(active_in=self.request.event, identifier=provider)
+
+        if self.request.POST.get("queue_sync") == "true":
+            prov.enqueue_order(self.order, 'user')
+            messages.success(self.request, _('The sync job has been enqueued and will run in the next minutes.'))
+        elif self.request.POST.get("cancel_job"):
+            job = self.order.queued_sync_jobs.get(pk=self.request.POST.get("cancel_job"))
+            if job.in_flight:
+                messages.warning(self.request, _('The sync job is already in progress.'))
+            else:
+                job.delete()
+                messages.success(self.request, _('The sync job has been canceled.'))
+        elif self.request.POST.get("run_job_now"):
+            job = self.order.queued_sync_jobs.get(pk=self.request.POST.get("run_job_now"))
+            job.not_before = now()
+            job.need_manual_retry = None
+            job.save()
+            messages.success(self.request, _('The sync job has been set to run as soon as possible.'))
+
+        return redirect(self.get_order_url())
+
+    def get(self, *args, **kwargs):
+        return HttpResponseNotAllowed(['POST'])
+
+
+class FailedSyncJobsView(ListView):
+    template_name = 'pretixcontrol/datasync/failed_jobs.html'
+    model = OrderSyncQueue
+    context_object_name = 'queue_items'
+    paginate_by = 100
+    ordering = ('triggered',)
+
+    def get_queryset(self):
+        return super().get_queryset().filter(
+            Q(need_manual_retry__isnull=False)
+            | Q(failed_attempts__gt=0)
+        ).select_related(
+            'order'
+        )
+
+    def post(self, request, *args, **kwargs):
+        items = self.get_queryset().filter(pk__in=request.POST.getlist('idlist'))
+
+        if self.request.POST.get("action") == "retry":
+            for item in items:
+                item.not_before = now()
+                item.need_manual_retry = None
+                item.save()
+            messages.success(self.request, _('The selected jobs have been set to run as soon as possible.'))
+        elif self.request.POST.get("action") == "cancel":
+            items.delete()
+            messages.success(self.request, _('The selected jobs have been canceled.'))
+
+        return redirect(request.get_full_path())
+
+
+class GlobalFailedSyncJobsView(AdministratorPermissionRequiredMixin, FailedSyncJobsView):
+    pass
+
+
+class OrganizerFailedSyncJobsView(OrganizerPermissionRequiredMixin, FailedSyncJobsView):
+    permission = "can_change_organizer_settings"
+
+    def get_queryset(self):
+        return super().get_queryset().filter(
+            event__organizer=self.request.organizer
+        )
+
+
+class EventFailedSyncJobsView(EventPermissionRequiredMixin, FailedSyncJobsView):
+    permission = "can_change_event_settings"
+
+    def get_queryset(self):
+        return super().get_queryset().filter(
+            event=self.request.event
+        )

src/tests/base/test_datasync.py

@@ -0,0 +1,611 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import json
+from collections import defaultdict, namedtuple
+from datetime import timedelta
+from decimal import Decimal
+
+import pytest
+from django.utils.timezone import now
+from django_scopes import scope
+
+from pretix.base.datasync.datasync import (
+    OutboundSyncProvider, StaticMapping, datasync_providers,
+)
+from pretix.base.datasync.utils import assign_properties
+from pretix.base.models import (
+    Event, InvoiceAddress, Item, Order, Organizer, Question,
+)
+from pretix.base.models.datasync import (
+    MODE_APPEND_LIST, MODE_OVERWRITE, MODE_SET_IF_EMPTY, MODE_SET_IF_NEW,
+)
+from pretix.base.services.datasync import sync_all
+
+
+@pytest.fixture(scope='function')
+def event():
+    o = Organizer.objects.create(name='Dummy', slug='dummy')
+    event = Event.objects.create(
+        organizer=o, name='Dummy', slug='dummy',
+        date_from=now(),
+        plugins='pretix.plugins.banktransfer,testplugin'
+    )
+    event.settings.name_scheme = 'given_family'
+    with scope(organizer=o):
+        ticket = Item.objects.create(event=event, name='Early-bird ticket',
+                                     default_price=Decimal('23.00'), admission=True)
+        question = ticket.questions.create(question="Whats's your favourite colour?", type=Question.TYPE_STRING,
+                                           event=event, required=False, identifier="FAV_COLOR")
+        question2 = ticket.questions.create(question="Food preference", type=Question.TYPE_CHOICE,
+                                            event=event, required=False, identifier="FOOD_PREF")
+        option1 = question2.options.create(identifier="F1", answer="vegetarian")
+        option2 = question2.options.create(identifier="F2", answer="vegan")
+
+        o1 = Order.objects.create(
+            code='1AAA', event=event, email='anonymous@example.org',
+            status=Order.STATUS_PENDING, locale='en',
+            datetime=now(), expires=now() + timedelta(days=10),
+            total=46,
+            sales_channel=event.organizer.sales_channels.get(identifier="web"),
+        )
+        op1 = o1.positions.create(
+            item=ticket, variation=None,
+            price=Decimal("23.00"), attendee_name_parts={'_scheme': 'given_family', 'given_name': "Alice", 'family_name': "Anonymous"}, positionid=1
+        )
+        op1.answers.create(question=question, answer="#3b1c4a")
+        op1.answers.create(question=question2, answer="vegan").options.set([option2])
+        op2 = o1.positions.create(
+            item=ticket, variation=None,
+            price=Decimal("23.00"), attendee_name_parts={'_scheme': 'given_family', 'given_name': "Charlie", 'family_name': "de l'Exemple"}, positionid=2
+        )
+        op2.answers.create(question=question, answer="Red")
+        op2.answers.create(question=question2, answer="vegetarian").options.set([option1])
+
+        o2 = Order.objects.create(
+            code='2EEE', event=event, email='ephemeral@example.com',
+            status=Order.STATUS_PENDING, locale='en',
+            datetime=now(), expires=now() + timedelta(days=10),
+            total=23,
+            sales_channel=event.organizer.sales_channels.get(identifier="web"),
+        )
+        o2.positions.create(
+            item=ticket, variation=None,
+            price=Decimal("23.00"), attendee_name_parts={'_scheme': 'given_family', 'given_name': "Eve", 'family_name': "Ephemeral"}, positionid=1
+        )
+        yield event
+
+
+def expected_order_sync_result():
+    return {
+        'ticketorders': [
+            {
+                '_id': 0,
+                'ordernumber': 'DUMMY-1AAA',
+                'orderemail': 'anonymous@example.org',
+                'status': 'pending',
+                'total': '46.00',
+                'payment_date': None,
+            },
+            {
+                '_id': 1,
+                'ordernumber': 'DUMMY-2EEE',
+                'orderemail': 'ephemeral@example.com',
+                'status': 'pending',
+                'total': '23.00',
+                'payment_date': None,
+            },
+        ],
+    }
+
+
+def expected_sync_result_with_associations():
+    return {
+        'tickets': [
+            {
+                '_id': 0,
+                'ticketnumber': '1AAA-1',
+                'amount': '23.00',
+                'firstname': 'Alice',
+                'lastname': 'Anonymous',
+                'status': 'pending',
+                'fav_color': '#3b1c4a',
+                'food': 'VEGAN',
+                'links': [],
+            },
+            {
+                '_id': 1,
+                'ticketnumber': '1AAA-2',
+                'amount': '23.00',
+                'firstname': 'Charlie',
+                'lastname': "de l'Exemple",
+                'status': 'pending',
+                'fav_color': 'Red',
+                'food': 'VEGETARIAN',
+                'links': [],
+            },
+            {
+                '_id': 2,
+                'ticketnumber': '2EEE-1',
+                'amount': '23.00',
+                'firstname': 'Eve',
+                'lastname': 'Ephemeral',
+                'status': 'pending',
+                'fav_color': '',
+                'food': '',
+                'links': [],
+            },
+        ],
+        'ticketorders': [
+            {
+                '_id': 0,
+                'ordernumber': 'DUMMY-1AAA',
+                'orderemail': 'anonymous@example.org',
+                'firstname': '',
+                'lastname': '',
+                'status': 'pending',
+                'links': ['link:tickets:0', 'link:tickets:1'],
+            },
+            {
+                '_id': 1,
+                'ordernumber': 'DUMMY-2EEE',
+                'orderemail': 'ephemeral@example.com',
+                'firstname': '',
+                'lastname': '',
+                'status': 'pending',
+                'links': ['link:tickets:2'],
+            },
+        ],
+    }
+
+
+def _register_with_fake_plugin_name(registry, obj, plugin_name):
+    registry.clear()
+
+    class App:
+        name = plugin_name
+    registry.register(obj)
+    registry.registered_entries[obj]['plugin'] = App
+
+
+class FakeSyncAPI:
+    def __init__(self):
+        self.fake_database = defaultdict(list)
+
+    def retrieve_object(self, table, search_by_attribute, search_for_value):
+        t = self.fake_database[table]
+        for idx, record in enumerate(t):
+            if record.get(search_by_attribute) == search_for_value:
+                return {**record, "_id": idx}
+        return None
+
+    def create_or_update_object(self, table, record):
+        t = self.fake_database[table]
+        if record.get("_id") is not None:
+            t[record["_id"]].update(record)
+        else:
+            record["_id"] = len(t)
+            t.append(record)
+        return record
+
+
+class SimpleOrderSync(OutboundSyncProvider):
+    identifier = "example1"
+    fake_api_client = None
+
+    @property
+    def mappings(self):
+        return [
+            StaticMapping(
+                id=1,
+                pretix_model='Order', external_object_type='ticketorders',
+                pretix_id_field='event_order_code', external_id_field='ordernumber',
+                property_mappings=json.dumps([
+                    {
+                        "pretix_field": "email",
+                        "external_field": "orderemail",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "order_status",
+                        "external_field": "status",
+                        "value_map": json.dumps({
+                            Order.STATUS_PENDING: "pending",
+                            Order.STATUS_PAID: "paid",
+                            Order.STATUS_EXPIRED: "expired",
+                            Order.STATUS_CANCELED: "canceled",
+                            Order.STATUS_REFUNDED: "refunded",
+                        }),
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "order_total",
+                        "external_field": "total",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "payment_date",
+                        "external_field": "payment_date",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                ])
+            )
+        ]
+
+    def sync_object_with_properties(
+            self,
+            external_id_field,
+            id_value,
+            properties: list,
+            inputs: dict,
+            mapping,
+            mapped_objects: dict,
+            **kwargs,
+    ):
+        pre_existing_object = self.fake_api_client.retrieve_object(mapping.external_object_type, external_id_field, id_value)
+        update_values = assign_properties(properties, pre_existing_object or {}, is_new=pre_existing_object is None, list_sep=";")
+        result = self.fake_api_client.create_or_update_object(mapping.external_object_type, {
+            **update_values,
+            external_id_field: id_value,
+            "_id": pre_existing_object and pre_existing_object.get("_id"),
+        })
+
+        return {
+            "object_type": mapping.external_object_type,
+            "external_id_field": external_id_field,
+            "id_value": id_value,
+            "external_link_href": f"https://external-system.example.com/backend/link/to/{mapping.external_object_type}/123/",
+            "external_link_display_name": "Contact #123 - Jane Doe",
+            "my_result": result,
+        }
+
+
+@pytest.mark.django_db
+def test_simple_order_sync(event):
+    _register_with_fake_plugin_name(datasync_providers, SimpleOrderSync, 'testplugin')
+
+    for order in event.orders.order_by("code").all():
+        SimpleOrderSync.enqueue_order(order, 'testcase')
+
+    SimpleOrderSync.fake_api_client = FakeSyncAPI()
+
+    sync_all()
+
+    expected = expected_order_sync_result()
+    assert SimpleOrderSync.fake_api_client.fake_database == expected
+
+    order_1a = event.orders.get(code='1AAA')
+    paydate = now()
+    order_1a.payments.create(payment_date=paydate, amount=order_1a.total)
+    order_1a.status = Order.STATUS_PAID
+    order_1a.save()
+
+    for order in event.orders.order_by("code").all():
+        SimpleOrderSync.enqueue_order(order, 'testcase')
+
+    sync_all()
+
+    expected['ticketorders'][0]['status'] = 'paid'
+    expected['ticketorders'][0]['payment_date'] = paydate.isoformat()
+    assert SimpleOrderSync.fake_api_client.fake_database == expected
+
+
+@pytest.mark.django_db
+def test_enqueue_order_twice(event):
+    _register_with_fake_plugin_name(datasync_providers, SimpleOrderSync, 'testplugin')
+
+    for order in event.orders.order_by("code").all():
+        SimpleOrderSync.enqueue_order(order, 'testcase_1st')
+
+    for order in event.orders.order_by("code").all():
+        SimpleOrderSync.enqueue_order(order, 'testcase_2nd')
+
+
+StaticMappingWithAssociations = namedtuple('StaticMappingWithAssociations', (
+    'id', 'pretix_model', 'external_object_type', 'pretix_id_field', 'external_id_field', 'property_mappings', 'association_mappings'
+))
+AssociationMapping = namedtuple('AssociationMapping', (
+    'via_mapping_id'
+))
+
+
+class OrderAndTicketAssociationSync(OutboundSyncProvider):
+    identifier = "example2"
+    fake_api_client = None
+
+    @property
+    def mappings(self):
+        return [
+            StaticMappingWithAssociations(
+                id=1,
+                pretix_model='OrderPosition', external_object_type='tickets',
+                pretix_id_field='ticket_id', external_id_field='ticketnumber',
+                property_mappings=json.dumps([
+                    {
+                        "pretix_field": "ticket_price",
+                        "external_field": "amount",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "attendee_name_given_name",
+                        "external_field": "firstname",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "attendee_name_family_name",
+                        "external_field": "lastname",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "order_status",
+                        "external_field": "status",
+                        "value_map": json.dumps({
+                            Order.STATUS_PENDING: "pending",
+                            Order.STATUS_PAID: "paid",
+                            Order.STATUS_EXPIRED: "expired",
+                            Order.STATUS_CANCELED: "canceled",
+                            Order.STATUS_REFUNDED: "refunded",
+                        }),
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "question_FAV_COLOR",
+                        "external_field": "fav_color",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "question_FOOD_PREF",
+                        "external_field": "food",
+                        "value_map": json.dumps({
+                            "F1": "VEGETARIAN",
+                            "F2": "VEGAN",
+                        }),
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                ]),
+                association_mappings=[],
+            ),
+            StaticMappingWithAssociations(
+                id=2,
+                pretix_model='Order', external_object_type='ticketorders',
+                pretix_id_field='event_order_code', external_id_field='ordernumber',
+                property_mappings=json.dumps([
+                    {
+                        "pretix_field": "email",
+                        "external_field": "orderemail",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "invoice_address_name_given_name",
+                        "external_field": "firstname",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "invoice_address_name_family_name",
+                        "external_field": "lastname",
+                        "value_map": "",
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                    {
+                        "pretix_field": "order_status",
+                        "external_field": "status",
+                        "value_map": json.dumps({
+                            Order.STATUS_PENDING: "pending",
+                            Order.STATUS_PAID: "paid",
+                            Order.STATUS_EXPIRED: "expired",
+                            Order.STATUS_CANCELED: "canceled",
+                            Order.STATUS_REFUNDED: "refunded",
+                        }),
+                        "overwrite": MODE_OVERWRITE,
+                    },
+                ]),
+                association_mappings=[
+                    AssociationMapping(via_mapping_id=1)
+                ],
+            ),
+        ]
+
+    def sync_object_with_properties(
+            self,
+            external_id_field,
+            id_value,
+            properties: list,
+            inputs: dict,
+            mapping,
+            mapped_objects: dict,
+            **kwargs,
+    ):
+        pre_existing_object = self.fake_api_client.retrieve_object(mapping.external_object_type, external_id_field, id_value)
+        update_values = assign_properties(properties, pre_existing_object or {}, is_new=pre_existing_object is None, list_sep=";")
+        result = self.fake_api_client.create_or_update_object(mapping.external_object_type, {
+            **update_values,
+            external_id_field: id_value,
+            "_id": pre_existing_object and pre_existing_object.get("_id"),
+            "links": [
+                f"link:{obj.external_object_type}:{obj.sync_info['my_result']['_id']}"
+                for am in mapping.association_mappings
+                for obj in mapped_objects[am.via_mapping_id]
+            ]
+        })
+
+        return {
+            "object_type": mapping.external_object_type,
+            "external_id_field": external_id_field,
+            "id_value": id_value,
+            "external_link_href": f"https://external-system.example.com/backend/link/to/{mapping.external_object_type}/123/",
+            "external_link_display_name": "Contact #123 - Jane Doe",
+            "my_result": result,
+        }
+
+
+@pytest.mark.django_db
+def test_association_sync(event):
+    _register_with_fake_plugin_name(datasync_providers, OrderAndTicketAssociationSync, 'testplugin')
+
+    for order in event.orders.order_by("code").all():
+        OrderAndTicketAssociationSync.enqueue_order(order, 'testcase')
+
+    OrderAndTicketAssociationSync.fake_api_client = FakeSyncAPI()
+
+    sync_all()
+
+    expected = expected_sync_result_with_associations()
+    assert OrderAndTicketAssociationSync.fake_api_client.fake_database == expected
+
+    order_1a = event.orders.get(code='1AAA')
+    order_1a.status = Order.STATUS_PAID
+    order_1a.save()
+
+    for order in event.orders.order_by("code").all():
+        OrderAndTicketAssociationSync.enqueue_order(order, 'testcase')
+
+    sync_all()
+
+    expected['tickets'][0]['status'] = 'paid'
+    expected['tickets'][1]['status'] = 'paid'
+    expected['ticketorders'][0]['status'] = 'paid'
+    assert OrderAndTicketAssociationSync.fake_api_client.fake_database == expected
+
+
+@pytest.mark.django_db
+def test_legacy_name_splitting(event):
+    _register_with_fake_plugin_name(datasync_providers, OrderAndTicketAssociationSync, 'testplugin')
+
+    for order in event.orders.order_by("code").all():
+        OrderAndTicketAssociationSync.enqueue_order(order, 'testcase')
+    InvoiceAddress.objects.create(order=order, name_parts={'_scheme': 'full', 'full_name': 'A B C D'})
+    order.refresh_from_db()
+    print(order.invoice_address.name_parts)
+    print(order.invoice_address.name)
+
+    event.settings.name_scheme = 'full'
+
+    OrderAndTicketAssociationSync.fake_api_client = FakeSyncAPI()
+
+    sync_all()
+
+    expected = expected_sync_result_with_associations()
+    expected['tickets'][1]['firstname'] = "Charlie de"  # yes, this splits incorrectly, hence it's legacy
+    expected['tickets'][1]['lastname'] = "l'Exemple"
+    expected['ticketorders'][1]['firstname'] = "A B C"
+    expected['ticketorders'][1]['lastname'] = "D"
+    assert OrderAndTicketAssociationSync.fake_api_client.fake_database == expected
+
+
+def test_assign_properties():
+    assert assign_properties(
+        [("name", "Alice", MODE_OVERWRITE)], {"name": "A"}, is_new=False, list_sep=";"
+    ) == {"name": "Alice"}
+    assert (
+        assign_properties([("name", "Alice", MODE_SET_IF_NEW)], {}, is_new=False, list_sep=";") == {}
+    )
+    assert assign_properties([("name", "Alice", MODE_SET_IF_NEW)], {}, is_new=True, list_sep=";") == {
+        "name": "Alice"
+    }
+    assert assign_properties(
+        [
+            ("name", "Alice", MODE_SET_IF_NEW),
+            ("name", "A", MODE_SET_IF_NEW),
+        ],
+        {},
+        is_new=True,
+        list_sep=";",
+    ) == {"name": "Alice"}
+    assert (
+        assign_properties(
+            [
+                ("name", "Alice", MODE_SET_IF_NEW),
+                ("name", "A", MODE_SET_IF_NEW),
+            ],
+            {"name": "Bob"},
+            is_new=False,
+            list_sep=";",
+        )
+        == {}
+    )
+    assert (
+        assign_properties(
+            [
+                ("name", "Alice", MODE_SET_IF_NEW),
+                ("name", "A", MODE_SET_IF_NEW),
+            ],
+            {},
+            is_new=False,
+            list_sep=";",
+        )
+        == {}
+    )
+    assert assign_properties(
+        [
+            ("name", "Alice", MODE_SET_IF_EMPTY),
+            ("name", "A", MODE_SET_IF_EMPTY),
+        ],
+        {},
+        is_new=True,
+        list_sep=";",
+    ) == {"name": "Alice"}
+    assert (
+        assign_properties(
+            [
+                ("name", "Alice", MODE_SET_IF_EMPTY),
+                ("name", "A", MODE_SET_IF_EMPTY),
+            ],
+            {"name": "Bob"},
+            is_new=False,
+            list_sep=";",
+        )
+        == {}
+    )
+    assert assign_properties(
+        [("name", "Alice", MODE_SET_IF_EMPTY)], {}, is_new=False, list_sep=";"
+    ) == {"name": "Alice"}
+
+    assert assign_properties(
+        [("name", "Alice", MODE_SET_IF_EMPTY)], {}, is_new=False, list_sep=";"
+    ) == {"name": "Alice"}
+
+    assert assign_properties(
+        [("colors", "red", MODE_APPEND_LIST)], {}, is_new=False, list_sep=";"
+    ) == {"colors": "red"}
+    assert assign_properties(
+        [("colors", "red", MODE_APPEND_LIST)], {"colors": "red"}, is_new=False, list_sep=";"
+    ) == {}
+    assert assign_properties(
+        [("colors", "red", MODE_APPEND_LIST)], {"colors": "blue"}, is_new=False, list_sep=";"
+    ) == {"colors": "blue;red"}
+    assert assign_properties(
+        [("colors", "red", MODE_APPEND_LIST)], {"colors": "green;blue"}, is_new=False, list_sep=";"
+    ) == {"colors": "green;blue;red"}
+    assert assign_properties(
+        [("colors", "red", MODE_APPEND_LIST)], {"colors": ["green", "blue"]}, is_new=False, list_sep=None
+    ) == {"colors": ["green", "blue", "red"]}
+    assert assign_properties(
+        [("colors", "green", MODE_APPEND_LIST)], {"colors": ["green", "blue"]}, is_new=False, list_sep=None
+    ) == {}