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pretix_cgo/doc/development/implementation/logging.rst
Mira c8d4815c9e LogEntryType registry (#4235)
Move display of LogEntry details from the `logentry_display` and 
`logentry_object_link` signals to a class hierarchy based approach. 
For each action_type, an instance of a subclass of `LogEntryType` 
is registered in the `log_entry_types` registry.

Analogous to EventPluginSignal, this registry is an `EventPluginRegistry`, 
so it keeps track of the plugin the LogEntryType is defined in.

---------

Co-authored-by: Raphael Michel <michel@rami.io>
Co-authored-by: Richard Schreiber <schreiber@rami.io>
2025-01-16 13:05:57 +01:00

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Logging and notifications
=========================
As pretix is handling monetary transactions, we are very careful to make it possible to review all changes
in the system that lead to the current state.
.. _`logging`:
Logging changes
---------------
We log data changes to the database in a format that makes it possible to display those logs to a human, if
required. pretix stores all those logs centrally in a model called :py:class:`pretix.base.models.LogEntry`.
We recommend all relevant models to inherit from ``LoggedModel`` as it simplifies creating new log entries:
.. autoclass:: pretix.base.models.LoggedModel
:members: log_action, all_logentries
To actually log an action, you can just call the ``log_action`` method on your object:
.. code-block:: python
order.log_action('pretix.event.order.comment', user=user,
data={"new_comment": "Hello, world."})
The positional ``action`` argument should represent the type of action and should be globally unique, we
recommend to prefix it with your package name, e.g. ``paypal.payment.rejected``. The ``user`` argument is
optional and may contain the user who performed the action. The optional ``data`` argument can contain
additional information about this action.
Logging form actions
""""""""""""""""""""
A very common use case is to log the changes to a model that have been done in a ``ModelForm``. In this case,
we generally use a custom ``form_valid`` method on our ``FormView`` that looks like this:
.. code-block:: python
@transaction.atomic
def form_valid(self, form):
if form.has_changed():
self.request.event.log_action('pretix.event.changed', user=self.request.user, data={
k: getattr(self.request.event, k) for k in form.changed_data
})
messages.success(self.request, _('Your changes have been saved.'))
return super().form_valid(form)
It gets a little bit more complicated if your form allows file uploads:
.. code-block:: python
@transaction.atomic
def form_valid(self, form):
if form.has_changed():
self.request.event.log_action(
'pretix.event.changed', user=self.request.user, data={
k: (form.cleaned_data.get(k).name
if isinstance(form.cleaned_data.get(k), File)
else form.cleaned_data.get(k))
for k in form.changed_data
}
)
messages.success(self.request, _('Your changes have been saved.'))
return super().form_valid(form)
Displaying logs
"""""""""""""""
If you want to display the logs of a particular object to a user in the backend, you can use the
following ready-to-include template::
{% include "pretixcontrol/includes/logs.html" with obj=order %}
We now need a way to translate the action codes like ``pretix.event.changed`` into human-readable
strings. The :py:attr:`pretix.base.logentrytypes.log_entry_types` :ref:`registry <registries>` allows you to do so. A simple
implementation could look like:
.. code-block:: python
from django.utils.translation import gettext as _
from pretix.base.logentrytypes import log_entry_types
@log_entry_types.new_from_dict({
'pretix.event.order.comment': _('The order\'s internal comment has been updated to: {new_comment}'),
'pretix.event.order.paid': _('The order has been marked as paid.'),
# ...
})
class CoreOrderLogEntryType(OrderLogEntryType):
pass
Please note that you always need to define your own inherited ``LogEntryType`` class in your plugin. If you would just
register an instance of a ``LogEntryType`` class defined in pretix core, it cannot be automatically detected as belonging
to your plugin, leading to confusing user interface situations.
Customizing log entry display
"""""""""""""""""""""""""""""
The base ``LogEntryType`` classes allow for varying degree of customization in their descendants.
If you want to add another log message for an existing core object (e.g. an :class:`Order <pretix.base.models.Order>`,
:class:`Item <pretix.base.models.Item>`, or :class:`Voucher <pretix.base.models.Voucher>`), you can inherit
from its predefined :class:`LogEntryType <pretix.base.logentrytypes.LogEntryType>`, e.g.
:class:`OrderLogEntryType <pretix.base.logentrytypes.OrderLogEntryType>`, and just specify a new plaintext string.
You can use format strings to insert information from the LogEntry's `data` object as shown in the section above.
If you define a new model object in your plugin, you should make sure proper object links in the user interface are
displayed for it. If your model object belongs logically to a pretix :class:`Event <pretix.base.models.Event>`, you can inherit from :class:`EventLogEntryType <pretix.base.logentrytypes.EventLogEntryType>`,
and set the ``object_link_*`` fields accordingly. ``object_link_viewname`` refers to a django url name, which needs to
accept the arguments `organizer` and `event`, containing the respective slugs, and additional arguments provided by
``object_link_args``. The default implementation of ``object_link_args`` will return an argument named by
````object_link_argname``, with a value of ``content_object.pk`` (the primary key of the model object).
If you want to customize the name displayed for the object (instead of the result of calling ``str()`` on it),
overwrite ``object_link_display_name``.
.. code-block:: python
class ItemLogEntryType(EventLogEntryType):
object_link_wrapper = _('Product {val}')
# link will be generated as reverse('control:event.item', {'organizer': ..., 'event': ..., 'item': item.pk})
object_link_viewname = 'control:event.item'
object_link_argname = 'item'
.. code-block:: python
class OrderLogEntryType(EventLogEntryType):
object_link_wrapper = _('Order {val}')
# link will be generated as reverse('control:event.order', {'organizer': ..., 'event': ..., 'code': order.code})
object_link_viewname = 'control:event.order'
def object_link_args(self, order):
return {'code': order.code}
def object_link_display_name(self, order):
return order.code
To show more sophisticated message strings, e.g. varying the message depending on information from the :class:`LogEntry <pretix.base.models.log.LogEntry>`'s
`data` object, override the `display` method:
.. code-block:: python
@log_entry_types.new()
class PaypalEventLogEntryType(EventLogEntryType):
action_type = 'pretix.plugins.paypal.event'
def display(self, logentry):
event_type = logentry.parsed_data.get('event_type')
text = {
'PAYMENT.SALE.COMPLETED': _('Payment completed.'),
'PAYMENT.SALE.DENIED': _('Payment denied.'),
# ...
}.get(event_type, f"({event_type})")
return _('PayPal reported an event: {}').format(text)
.. automethod:: pretix.base.logentrytypes.LogEntryType.display
If your new model object does not belong to an :class:`Event <pretix.base.models.Event>`, you need to inherit directly from ``LogEntryType`` instead
of ``EventLogEntryType``, providing your own implementation of ``get_object_link_info`` if object links should be
displayed.
.. autoclass:: pretix.base.logentrytypes.LogEntryType
:members: get_object_link_info
Sending notifications
---------------------
If you think that the logged information might be important or urgent enough to send out a notification to interested
organizers. In this case, you should listen for the :py:attr:`pretix.base.signals.register_notification_types` signal
to register a notification type:
.. code-block:: python
@receiver(register_notification_types)
def register_my_notification_types(sender, **kwargs):
return [MyNotificationType(sender)]
Note that this event is different than other events send out by pretix: ``sender`` may be an event or ``None``. The
latter case is required to let the user define global notification preferences for all events.
You also need to implement a custom class that specifies how notifications should be handled for your notification type.
You should subclass the base ``NotificationType`` class and implement all its members:
.. autoclass:: pretix.base.notifications.NotificationType
:members: action_type, verbose_name, required_permission, build_notification
A simple implementation could look like this:
.. code-block:: python
class MyNotificationType(NotificationType):
required_permission = "can_view_orders"
action_type = "pretix.event.order.paid"
verbose_name = _("Order has been paid")
def build_notification(self, logentry: LogEntry):
order = logentry.content_object
order_url = build_absolute_uri(
'control:event.order',
kwargs={
'organizer': logentry.event.organizer.slug,
'event': logentry.event.slug,
'code': order.code
}
)
n = Notification(
event=logentry.event,
title=_('Order {code} has been marked as paid').format(code=order.code),
url=order_url
)
n.add_attribute(_('Order code'), order.code)
n.add_action(_('View order details'), order_url)
return n
As you can see, the relevant code is in the ``build_notification`` method that is supposed to create a ``Notification``
method that has a title, description, URL, attributes, and actions. The full definition of ``Notification`` is the
following:
.. autoclass:: pretix.base.notifications.Notification
:members: add_action, add_attribute
Logging technical information
-----------------------------
If you just want to log technical information to a log file on disk that does not need to be parsed
and displayed later, you can just use Python's ``logging`` module:
.. code-block:: python
import logging
logger = logging.getLogger(__name__)
logger.info('Startup complete.')
This is also very useful to provide debugging information when an exception occurs:
.. code-block:: python
try:
foo()
except:
logger.exception('Error when calling foo()') # Traceback will automatically be appended
messages.error(request, _('An error occured.'))