Change semantics of changing orders

This basically does two things to the "Change products" view of orders and the
OrderChangeManager program API:

1) It decouples changing items or subevents from changing prices.
   OrderChangeManager.change_item() and .change_subevent() no longer
   touch the price of a position. Instead .change_price() needs to be
   called explicitly. However, a client-side JavaScript component now
   *proposes* a new price based on the changed item or subevent.

2) The user interface now exposes the possibility of doing multiple
   things at the same time, i.e. changing the item, subevent and price
   in the same operation. OrderChangeManager already allowed this
   before.

(1) is basically a consequence of (2), while (2) is a prerequesite for
e.g. the `seating` branch, where changing the subevent will always
require changing the seat.

src/pretix/api/serializers/order.py

@@ -14,8 +14,8 @@ from pretix.api.serializers.i18n import I18nAwareModelSerializer
 from pretix.base.channels import get_all_sales_channels
 from pretix.base.i18n import language
 from pretix.base.models import (
-    Checkin, Invoice, InvoiceAddress, InvoiceLine, Order, OrderPosition,
+    Checkin, Invoice, InvoiceAddress, InvoiceLine, Item, ItemVariation, Order,
-    Question, QuestionAnswer,
+    OrderPosition, Question, QuestionAnswer, SubEvent,
 )
 from pretix.base.models.orders import (
     CartPosition, OrderFee, OrderPayment, OrderRefund,
@@ -288,6 +288,23 @@ class OrderSerializer(I18nAwareModelSerializer):
         return instance
 
 
+class PriceCalcSerializer(serializers.Serializer):
+    item = serializers.PrimaryKeyRelatedField(queryset=Item.objects.none(), required=False, allow_null=True)
+    variation = serializers.PrimaryKeyRelatedField(queryset=ItemVariation.objects.none(), required=False, allow_null=True)
+    subevent = serializers.PrimaryKeyRelatedField(queryset=SubEvent.objects.none(), required=False, allow_null=True)
+    locale = serializers.CharField(allow_null=True, required=False)
+
+    def __init__(self, *args, **kwargs):
+        event = kwargs.pop('event')
+        super().__init__(*args, **kwargs)
+        self.fields['item'].queryset = event.items.all()
+        self.fields['variation'].queryset = ItemVariation.objects.filter(item__event=event)
+        if event.has_subevents:
+            self.fields['subevent'].queryset = event.subevents.all()
+        else:
+            del self.fields['subevent']
+
+
 class AnswerCreateSerializer(I18nAwareModelSerializer):
 
     class Meta:

src/pretix/api/views/order.py

@@ -24,11 +24,12 @@ from pretix.api.models import OAuthAccessToken
 from pretix.api.serializers.order import (
     InvoiceSerializer, OrderCreateSerializer, OrderPaymentSerializer,
     OrderPositionSerializer, OrderRefundCreateSerializer,
-    OrderRefundSerializer, OrderSerializer,
+    OrderRefundSerializer, OrderSerializer, PriceCalcSerializer,
 )
+from pretix.base.i18n import language
 from pretix.base.models import (
-    CachedCombinedTicket, CachedTicket, Device, Event, Invoice, Order,
+    CachedCombinedTicket, CachedTicket, Device, Event, Invoice, InvoiceAddress,
-    OrderPayment, OrderPosition, OrderRefund, Quota, TeamAPIToken,
+    Order, OrderPayment, OrderPosition, OrderRefund, Quota, TeamAPIToken,
     generate_position_secret, generate_secret,
 )
 from pretix.base.payment import PaymentException
@@ -42,10 +43,12 @@ from pretix.base.services.orders import (
     OrderChangeManager, OrderError, approve_order, cancel_order, deny_order,
     extend_order, mark_order_expired, mark_order_refunded,
 )
+from pretix.base.services.pricing import get_price
 from pretix.base.services.tickets import generate
 from pretix.base.signals import (
     order_modified, order_placed, register_ticket_outputs,
 )
+from pretix.base.templatetags.money import money_filter
 
 
 class OrderFilter(FilterSet):
@@ -622,6 +625,82 @@ class OrderPositionViewSet(mixins.DestroyModelMixin, viewsets.ReadOnlyModelViewS
                 return prov
         raise NotFound('Unknown output provider.')
 
+    @action(detail=True, methods=['POST'], url_name='price_calc')
+    def price_calc(self, request, *args, **kwargs):
+        """
+        This calculates the price assuming a change of product or subevent. This endpoint
+        is deliberately not documented and considered a private API, only to be used by
+        pretix' web interface.
+
+        Sample input:
+
+        {
+            "item": 2,
+            "variation": null,
+            "subevent": 3
+        }
+
+        Sample output:
+
+        {
+            "gross": "2.34",
+            "gross_formatted": "2,34",
+            "net": "2.34",
+            "tax": "0.00",
+            "rate": "0.00",
+            "name": "VAT"
+        }
+        """
+        serializer = PriceCalcSerializer(data=request.data, event=request.event)
+        serializer.is_valid(raise_exception=True)
+        data = serializer.validated_data
+        pos = self.get_object()
+
+        try:
+            ia = pos.order.invoice_address
+        except InvoiceAddress.DoesNotExist:
+            ia = InvoiceAddress()
+
+        kwargs = {
+            'item': pos.item,
+            'variation': pos.variation,
+            'voucher': pos.voucher,
+            'subevent': pos.subevent,
+            'addon_to': pos.addon_to,
+            'invoice_address': ia,
+        }
+
+        if data.get('item'):
+            item = data.get('item')
+            kwargs['item'] = item
+
+            if item.has_variations:
+                variation = data.get('variation') or pos.variation
+                if not variation:
+                    raise ValidationError('No variation given')
+                if variation.item != item:
+                    raise ValidationError('Variation does not belong to item')
+            else:
+                variation = None
+                kwargs['variation'] = None
+
+            if pos.voucher and not pos.voucher.applies_to(item, variation):
+                kwargs['voucher'] = None
+
+        if data.get('subevent'):
+            kwargs['subevent'] = data.get('subevent')
+
+        price = get_price(**kwargs)
+        with language(data.get('locale') or self.request.event.settings.locale):
+            return Response({
+                'gross': price.gross,
+                'gross_formatted': money_filter(price.gross, self.request.event.currency, hide_currency=True),
+                'net': price.net,
+                'rate': price.rate,
+                'name': str(price.name),
+                'tax': price.tax,
+            })
+
     @action(detail=True, url_name='download', url_path='download/(?P<output>[^/]+)')
     def download(self, request, output, **kwargs):
         provider = self._get_output_provider(output)

src/pretix/base/services/orders.py

@@ -846,8 +846,8 @@ class OrderChangeManager:
         'addon_invalid': _('The selected base position does not allow you to add this product as an add-on.'),
         'subevent_required': _('You need to choose a subevent for the new position.'),
     }
-    ItemOperation = namedtuple('ItemOperation', ('position', 'item', 'variation', 'price'))
+    ItemOperation = namedtuple('ItemOperation', ('position', 'item', 'variation'))
-    SubeventOperation = namedtuple('SubeventOperation', ('position', 'subevent', 'price'))
+    SubeventOperation = namedtuple('SubeventOperation', ('position', 'subevent'))
     PriceOperation = namedtuple('PriceOperation', ('position', 'price'))
     CancelOperation = namedtuple('CancelOperation', ('position',))
     AddOperation = namedtuple('AddOperation', ('item', 'variation', 'price', 'addon_to', 'subevent'))
@@ -867,33 +867,18 @@ class OrderChangeManager:
         self.notify = notify
         self._invoice_dirty = False
 
-    def change_item(self, position: OrderPosition, item: Item, variation: Optional[ItemVariation], keep_price=False):
+    def change_item(self, position: OrderPosition, item: Item, variation: Optional[ItemVariation]):
         if (not variation and item.has_variations) or (variation and variation.item_id != item.pk):
             raise OrderError(self.error_messages['product_without_variation'])
 
-        if keep_price:
-            price = TaxedPrice(gross=position.price, net=position.price - position.tax_value,
-                               tax=position.tax_value, rate=position.tax_rate,
-                               name=position.tax_rule.name if position.tax_rule else None)
-        else:
-            price = get_price(item, variation, voucher=position.voucher, subevent=position.subevent,
-                              invoice_address=self._invoice_address)
-
-        if price is None:  # NOQA
-            raise OrderError(self.error_messages['product_invalid'])
-
         new_quotas = (variation.quotas.filter(subevent=position.subevent)
                       if variation else item.quotas.filter(subevent=position.subevent))
         if not new_quotas:
             raise OrderError(self.error_messages['quota_missing'])
 
-        if self.order.event.settings.invoice_include_free or price.gross != Decimal('0.00') or position.price != Decimal('0.00'):
-            self._invoice_dirty = True
-
-        self._totaldiff += price.gross - position.price
         self._quotadiff.update(new_quotas)
         self._quotadiff.subtract(position.quotas)
-        self._operations.append(self.ItemOperation(position, item, variation, price))
+        self._operations.append(self.ItemOperation(position, item, variation))
 
     def change_subevent(self, position: OrderPosition, subevent: SubEvent):
         price = get_price(position.item, position.variation, voucher=position.voucher, subevent=subevent,
@@ -907,19 +892,15 @@ class OrderChangeManager:
         if not new_quotas:
             raise OrderError(self.error_messages['quota_missing'])
 
-        if self.order.event.settings.invoice_include_free or price.gross != Decimal('0.00') or position.price != Decimal('0.00'):
-            self._invoice_dirty = True
-
-        self._totaldiff += price.gross - position.price
         self._quotadiff.update(new_quotas)
         self._quotadiff.subtract(position.quotas)
-        self._operations.append(self.SubeventOperation(position, subevent, price))
+        self._operations.append(self.SubeventOperation(position, subevent))
 
     def regenerate_secret(self, position: OrderPosition):
         self._operations.append(self.RegenerateSecretOperation(position))
 
     def change_price(self, position: OrderPosition, price: Decimal):
-        price = position.item.tax(price)
+        price = position.item.tax(price, base_price_is='gross')
 
         self._totaldiff += price.gross - position.price
 
@@ -1076,14 +1057,11 @@ class OrderChangeManager:
                     'new_variation': op.variation.pk if op.variation else None,
                     'old_price': op.position.price,
                     'addon_to': op.position.addon_to_id,
-                    'new_price': op.price.gross
+                    'new_price': op.position.price
                 })
                 op.position.item = op.item
                 op.position.variation = op.variation
-                op.position.price = op.price.gross
+                op.position._calculate_tax()
-                op.position.tax_rate = op.price.rate
-                op.position.tax_value = op.price.tax
-                op.position.tax_rule = op.item.tax_rule
                 op.position.save()
             elif isinstance(op, self.SubeventOperation):
                 self.order.log_action('pretix.event.order.changed.subevent', user=self.user, auth=self.auth, data={
@@ -1092,13 +1070,9 @@ class OrderChangeManager:
                     'old_subevent': op.position.subevent.pk,
                     'new_subevent': op.subevent.pk,
                     'old_price': op.position.price,
-                    'new_price': op.price.gross
+                    'new_price': op.position.price
                 })
                 op.position.subevent = op.subevent
-                op.position.price = op.price.gross
-                op.position.tax_rate = op.price.rate
-                op.position.tax_value = op.price.tax
-                op.position.tax_rule = op.position.item.tax_rule
                 op.position.save()
             elif isinstance(op, self.PriceOperation):
                 self.order.log_action('pretix.event.order.changed.price', user=self.user, auth=self.auth, data={
@@ -1109,9 +1083,7 @@ class OrderChangeManager:
                     'new_price': op.price.gross
                 })
                 op.position.price = op.price.gross
-                op.position.tax_rate = op.price.rate
+                op.position._calculate_tax()
-                op.position.tax_value = op.price.tax
-                op.position.tax_rule = op.position.item.tax_rule
                 op.position.save()
             elif isinstance(op, self.CancelOperation):
                 for opa in op.position.addons.all():

src/pretix/control/forms/orders.py

@@ -9,9 +9,7 @@ from django.utils.timezone import now
 from django.utils.translation import pgettext_lazy, ugettext_lazy as _
 
 from pretix.base.forms import I18nModelForm, PlaceholderValidator
-from pretix.base.models import (
+from pretix.base.models import InvoiceAddress, ItemAddOn, Order, OrderPosition
-    InvoiceAddress, Item, ItemAddOn, Order, OrderPosition,
-)
 from pretix.base.models.event import SubEvent
 from pretix.base.services.pricing import get_price
 from pretix.control.forms.widgets import Select2
@@ -150,15 +148,6 @@ class CommentForm(I18nModelForm):
         }
 
 
-class SubEventChoiceField(forms.ModelChoiceField):
-    def label_from_instance(self, obj):
-        p = get_price(self.instance.item, self.instance.variation,
-                      voucher=self.instance.voucher,
-                      subevent=obj)
-        return '{} – {} ({})'.format(obj.name, obj.get_date_range_display(),
-                                     p.print(self.instance.order.event.currency))
-
-
 class OtherOperationsForm(forms.Form):
     recalculate_taxes = forms.BooleanField(
         label=_('Re-calculate taxes'),
@@ -265,12 +254,13 @@ class OrderPositionAddForm(forms.Form):
 
 
 class OrderPositionChangeForm(forms.Form):
-    itemvar = forms.ChoiceField()
+    itemvar = forms.ChoiceField(
-    subevent = SubEventChoiceField(
+        required=False,
+    )
+    subevent = forms.ModelChoiceField(
         SubEvent.objects.none(),
-        label=pgettext_lazy('subevent', 'New date'),
+        required=False,
-        required=True,
+        empty_label=_('(Unchanged)')
-        empty_label=None
     )
     price = forms.DecimalField(
         required=False,
@@ -278,53 +268,49 @@ class OrderPositionChangeForm(forms.Form):
         localize=True,
         label=_('New price (gross)')
     )
-    operation = forms.ChoiceField(
+    operation_secret = forms.BooleanField(
         required=False,
-        widget=forms.RadioSelect,
+        label=_('Generate a new secret')
-        choices=(
+    )
-            ('product', 'Change product'),
+    operation_cancel = forms.BooleanField(
-            ('price', 'Change price'),
+        required=False,
-            ('subevent', 'Change event date'),
+        label=_('Cancel this position')
-            ('cancel', 'Remove product'),
+    )
-            ('split', 'Split into new order'),
+    operation_split = forms.BooleanField(
-            ('secret', 'Regenerate secret'),
+        required=False,
-        )
+        label=_('Split into new order')
     )
-    change_product_keep_price = forms.BooleanField(required=False)
 
     def __init__(self, *args, **kwargs):
         instance = kwargs.pop('instance')
         initial = kwargs.get('initial', {})
 
-        try:
+        if instance.item.tax_rule and not instance.item.tax_rule.price_includes_tax:
-            ia = instance.order.invoice_address
+            initial['price'] = instance.price - instance.tax_value
-        except InvoiceAddress.DoesNotExist:
+        else:
-            ia = None
+            initial['price'] = instance.price
-
-        if instance:
-            try:
-                if instance.variation:
-                    initial['itemvar'] = '%d-%d' % (instance.item.pk, instance.variation.pk)
-                elif instance.item:
-                    initial['itemvar'] = str(instance.item.pk)
-            except Item.DoesNotExist:
-                pass
-
-            if instance.item.tax_rule and not instance.item.tax_rule.price_includes_tax:
-                initial['price'] = instance.price - instance.tax_value
-            else:
-                initial['price'] = instance.price
-        initial['subevent'] = instance.subevent
 
         kwargs['initial'] = initial
         super().__init__(*args, **kwargs)
         if instance.order.event.has_subevents:
-            self.fields['subevent'].instance = instance
             self.fields['subevent'].queryset = instance.order.event.subevents.all()
+            self.fields['subevent'].widget = Select2(
+                attrs={
+                    'data-model-select2': 'event',
+                    'data-select2-url': reverse('control:event.subevents.select2', kwargs={
+                        'event': instance.order.event.slug,
+                        'organizer': instance.order.event.organizer.slug,
+                    }),
+                    'data-placeholder': _('(Unchanged)')
+                }
+            )
+            self.fields['subevent'].widget.choices = self.fields['subevent'].choices
         else:
             del self.fields['subevent']
 
-        choices = []
+        choices = [
+            ('', _('(Unchanged)'))
+        ]
         for i in instance.order.event.items.prefetch_related('variations').all():
             pname = str(i)
             if not i.is_available():
@@ -333,14 +319,10 @@ class OrderPositionChangeForm(forms.Form):
 
             if variations:
                 for v in variations:
-                    p = get_price(i, v, voucher=instance.voucher, subevent=instance.subevent,
-                                  invoice_address=ia)
                     choices.append(('%d-%d' % (i.pk, v.pk),
-                                    '%s – %s (%s)' % (pname, v.value, p.print(instance.order.event.currency))))
+                                    '%s – %s' % (pname, v.value)))
             else:
-                p = get_price(i, None, voucher=instance.voucher, subevent=instance.subevent,
+                choices.append((str(i.pk), pname))
-                              invoice_address=ia)
-                choices.append((str(i.pk), '%s (%s)' % (pname, p.print(instance.order.event.currency))))
         self.fields['itemvar'].choices = choices
         change_decimal_field(self.fields['price'], instance.order.event.currency)
 

src/pretix/control/templates/pretixcontrol/base.html

@@ -43,6 +43,7 @@
             <script type="text/javascript" src="{% static "pretixcontrol/js/ui/subevent.js" %}"></script>
             <script type="text/javascript" src="{% static "pretixcontrol/js/ui/question.js" %}"></script>
             <script type="text/javascript" src="{% static "pretixcontrol/js/ui/mail.js" %}"></script>
+            <script type="text/javascript" src="{% static "pretixcontrol/js/ui/orderchange.js" %}"></script>
             <script type="text/javascript" src="{% static "pretixcontrol/js/ui/typeahead.js" %}"></script>
             <script type="text/javascript" src="{% static "pretixcontrol/js/ui/quicksetup.js" %}"></script>
             <script type="text/javascript" src="{% static "pretixbase/js/details.js" %}"></script>

src/pretix/control/templates/pretixcontrol/order/change.html

@@ -1,6 +1,7 @@
 {% extends "pretixcontrol/event/base.html" %}
 {% load i18n %}
 {% load bootstrap3 %}
+{% load money %}
 {% block title %}
     {% blocktrans trimmed with code=order.code %}
         Change order: {{ code }}
@@ -71,92 +72,87 @@
                     </h3>
                 </div>
                 <div class="panel-body">
-                    <div class="form-inline form-order-change">
+                    <div class="form-order-change" data-pricecalc-endpoint="{% url "api-v1:orderposition-price_calc" organizer=order.event.organizer.slug event=order.event.slug pk=position.pk %}">
                         {% bootstrap_form_errors position.form %}
                         {% if position.custom_error %}
                             <div class="alert alert-danger">
                                 {{ position.custom_error }}
                             </div>
                         {% endif %}
-                        <p class="help-block">
+                        <div class="row">
-                            {% trans "Ticket secret:" %} {{ position.secret|slice:":12" }}…
+                            <div class="col-sm-5 col-sm-offset-3">
-                        </p>
+                                <strong>{% trans "Current value" %}</strong>
-                        <div class="radio">
+                            </div>
-                            <label>
+                            <div class="col-sm-4">
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value=""
+                                <strong>{% trans "Change to" %}</strong>
-                                        {% if not position.form.operation.value %}checked="checked"{% endif %}>
+                            </div>
-                                {% trans "Keep unchanged" %}
-                            </label>
                         </div>
-                        <div class="radio">
+                        <div class="row">
-                            <label>
+                            <div class="col-sm-3">
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value="product"
+                                <strong>{% trans "Product" %}</strong>
-                                        {% if position.form.operation.value == "product" %}checked="checked"{% endif %}>
+                            </div>
-                                {% trans "Change product to" %}
+                            <div class="col-sm-5">
+                                {{ position.item }}
+                                {% if position.variation %}
+                                    – {{ position.variation }}
+                                {% endif %}
+                            </div>
+                            <div class="col-sm-4">
                                 {% bootstrap_field position.form.itemvar layout='inline' %}
-                            </label>
+                            </div>
-                            <label class="checkbox">
-                                {{ position.form.change_product_keep_price }}
-                                {% trans "Keep price the same" %}
-                            </label>
                         </div>
+
                         {% if request.event.has_subevents %}
-                            <div class="radio">
+                            <div class="row">
-                                <label>
+                                <div class="col-sm-3">
-                                    <input name="{{ position.form.prefix }}-operation" type="radio" value="subevent"
+                                    <strong>{% trans "Date" context "subevent" %}</strong>
-                                            {% if position.form.operation.value == "subevent" %}checked="checked"{% endif %}>
+                                </div>
-                                    {% trans "Change date to" context "subevent" %}
+                                <div class="col-sm-5">
+                                    {{ position.subevent }}
+                                </div>
+                                <div class="col-sm-4">
                                     {% bootstrap_field position.form.subevent layout='inline' %}
-                                </label>
+                                </div>
                             </div>
                         {% endif %}
-                        <div class="radio">
+
-                            <label>
+                        <div class="row">
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value="price"
+                            <div class="col-sm-3">
-                                        {% if position.form.operation.value == "price" %}checked="checked"{% endif %}>
+                                <strong>{% trans "Price" %}</strong>
-                                {% trans "Change price to" %}
+                            </div>
+                            <div class="col-sm-5">
+                                {{ position.price|money:request.event.currency }}<br>
+                                {% if position.tax_rate %}
+                                    <small>{% blocktrans trimmed with rate=position.tax_rate name=position.tax_rule.name %}
+                                        <strong>incl.</strong> {{ rate }}% {{ name }}
+                                    {% endblocktrans %}</small>
+                                {% endif %}
+                            </div>
+                            <div class="col-sm-4 field-container">
                                 {% bootstrap_field position.form.price addon_after=request.event.currency layout='inline' %}
-                                {% if position.apply_tax %}
+                                <small><strong>{% trans "including all taxes" %}</strong></small>
-                                    {% if position.item.tax_rule and not position.item.tax_rule.price_includes_tax %}
+                            </div>
-                                        {% blocktrans trimmed with rate=position.item.tax_rule.rate name=position.item.tax_rule.name %}
-                                            <strong>plus</strong> {{ rate }}% {{ name }}
-                                        {% endblocktrans %}
-                                    {% elif position.item.tax_rule %}
-                                        {% blocktrans trimmed with rate=position.item.tax_rule.rate name=position.item.tax_rule.name %}
-                                            <strong>incl.</strong> {{ rate }}% {{ name }}
-                                        {% endblocktrans %}
-                                    {% endif %}
-                                {% else %}
-                                    {% trans "no taxes apply" %}
-                                {% endif %}
-                            </label>
                         </div>
-                        <div class="radio">
+
-                            <label>
+                        <div class="row">
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value="split"
+                            <div class="col-sm-3">
-                                        {% if position.form.operation.value == "split" %}checked="checked"{% endif %}>
+                                <strong>{% trans "Ticket secret" %}</strong>
-                                {% trans "Split into new order" %}
+                            </div>
-                            </label>
+                            <div class="col-sm-5">
-                        </div>
+                                {{ position.secret|slice:":12" }}…
-                        <div class="radio">
+                            </div>
-                            <label>
+                            <div class="col-sm-4">
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value="secret"
+                                {% bootstrap_field position.form.operation_secret layout='inline' %}
-                                        {% if position.form.operation.value == "secret" %}checked="checked"{% endif %}>
+                            </div>
-                                {% trans "Generate a new secret" %}
-                            </label>
-                        </div>
-                        <div class="radio">
-                            <label>
-                                <input name="{{ position.form.prefix }}-operation" type="radio" value="cancel"
-                                        {% if position.form.operation.value == "cancel" %}checked="checked"{% endif %}>
-                                {% trans "Cancel position" %}
-                                {% if position.addons.exists %}
-                                    <em class="text-danger">
-                                        {% trans "Removing this position will also remove all add-ons to this position." %}
-                                    </em>
-                                {% endif %}
-                            </label>
                         </div>
+
+                        {% bootstrap_field position.form.operation_cancel layout='inline' %}
+                        {% bootstrap_field position.form.operation_split layout='inline' %}
+                        {% if position.addons.exists %}
+                            <em class="text-danger">
+                                {% trans "Removing this position will also remove all add-ons to this position." %}
+                            </em>
+                        {% endif %}
                     </div>
                 </div>
             </div>

src/pretix/control/views/orders.py

@@ -1240,7 +1240,11 @@ class OrderChange(OrderView):
                 return False
 
             try:
-                if p.form.cleaned_data['operation'] == 'product':
+                if p.form.cleaned_data['operation_cancel']:
+                    ocm.cancel(p)
+                    continue
+
+                if p.form.cleaned_data['itemvar']:
                     if '-' in p.form.cleaned_data['itemvar']:
                         itemid, varid = p.form.cleaned_data['itemvar'].split('-')
                     else:
@@ -1251,16 +1255,19 @@ class OrderChange(OrderView):
                         variation = ItemVariation.objects.get(pk=varid, item=item)
                     else:
                         variation = None
-                    ocm.change_item(p, item, variation, keep_price=p.form.cleaned_data['change_product_keep_price'])
+                    if item != p.item or variation != p.variation:
-                elif p.form.cleaned_data['operation'] == 'price':
+                        ocm.change_item(p, item, variation)
-                    ocm.change_price(p, p.form.cleaned_data['price'])
+
-                elif p.form.cleaned_data['operation'] == 'subevent':
+                if self.request.event.has_subevents and p.form.cleaned_data['subevent'] and p.form.cleaned_data['subevent'] != p.subevent:
                     ocm.change_subevent(p, p.form.cleaned_data['subevent'])
-                elif p.form.cleaned_data['operation'] == 'cancel':
+
-                    ocm.cancel(p)
+                if p.form.cleaned_data['price'] != p.price:
-                elif p.form.cleaned_data['operation'] == 'split':
+                    ocm.change_price(p, p.form.cleaned_data['price'])
+
+                if p.form.cleaned_data['operation_split']:
                     ocm.split(p)
-                elif p.form.cleaned_data['operation'] == 'secret':
+
+                if p.form.cleaned_data['operation_secret']:
                     ocm.regenerate_secret(p)
 
             except OrderError as e:

src/pretix/static/pretixcontrol/js/ui/orderchange.js

@@ -0,0 +1,51 @@
+/*global $, gettext*/
+$(function () {
+    // Question view
+    if (!$(".form-order-change").length) {
+        return;
+    }
+    $(".form-order-change").each(function () {
+        var url = $(this).attr("data-pricecalc-endpoint");
+        var $itemvar = $(this).find("[name*=itemvar]");
+        var $subevent = $(this).find("[name*=subevent]");
+        var $price = $(this).find("[name*=price]");
+        var update_price = function () {
+            console.log(url);
+            var itemvar = $itemvar.val();
+            var item = null;
+            var variation = null;
+            if (itemvar.indexOf("-")) {
+                item = parseInt(itemvar.split("-")[0]);
+                variation = parseInt(itemvar.split("-")[1]);
+            } else {
+                item = parseInt(itemvar);
+            }
+            $price.closest(".field-container").append("<small class=\"loading-indicator\"><span class=\"fa fa-cog fa-spin\"></span> " +
+                gettext("Calculating default price…") + "</small>");
+            $.ajax(
+                {
+                    'type': 'POST',
+                    'url': url,
+                    'headers': {'X-CSRFToken': $("input[name=csrfmiddlewaretoken]").val()},
+                    'data': JSON.stringify({
+                        'item': item,
+                        'variation': variation,
+                        'subevent': $subevent.val(),
+                        'locale': $("body").attr("data-pretixlocale"),
+                    }),
+                    'contentType': "application/json",
+                    'success': function (data) {
+                        $price.val(data.gross_formatted);
+                        $price.closest(".field-container").find(".loading-indicator").remove();
+                    },
+                    // 'error': …
+                    'context': this,
+                    'dataType': 'json',
+                    'timeout': 30000
+                }
+            );
+        };
+        $itemvar.on("change", update_price);
+        $subevent.on("change", update_price);
+    });
+});

src/pretix/static/pretixcontrol/scss/_forms.scss

@@ -407,6 +407,12 @@ table td > .checkbox input[type="checkbox"] {
   }
 }
 
+.form-order-change {
+  .row {
+    padding: 5px 0;
+  }
+}
+
 @media(max-width: $screen-xs-max) {
   .nameparts-form-group {
     display: block;
@@ -455,3 +461,4 @@ table td > .checkbox input[type="checkbox"] {
     }
   }
 }
+

src/tests/base/test_orders.py

@@ -611,49 +611,27 @@ class OrderChangeManagerTests(TestCase):
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
         assert self.op1.subevent == se2
-        assert self.op1.price == 12
+        assert self.op1.price == Decimal('23.00')
         assert self.order.total == self.op1.price + self.op2.price
 
-    def test_change_subevent_reverse_charge(self):
+    def test_change_subevent_with_price_success(self):
-        self._enable_reverse_charge()
         self.event.has_subevents = True
         self.event.save()
         se1 = self.event.subevents.create(name="Foo", date_from=now())
         se2 = self.event.subevents.create(name="Bar", date_from=now())
-        SubEventItem.objects.create(subevent=se2, item=self.ticket, price=10.7)
+        SubEventItem.objects.create(subevent=se2, item=self.ticket, price=12)
         self.op1.subevent = se1
         self.op1.save()
         self.quota.subevent = se2
         self.quota.save()
 
         self.ocm.change_subevent(self.op1, se2)
+        self.ocm.change_price(self.op1, Decimal('12.00'))
         self.ocm.commit()
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
         assert self.op1.subevent == se2
-        assert self.op1.price == Decimal('10.00')
+        assert self.op1.price == Decimal('12.00')
-        assert self.op1.tax_value == Decimal('0.00')
-        assert self.order.total == self.op1.price + self.op2.price
-
-    def test_change_subevent_net_price(self):
-        self.event.has_subevents = True
-        self.event.save()
-        se1 = self.event.subevents.create(name="Foo", date_from=now())
-        se2 = self.event.subevents.create(name="Bar", date_from=now())
-        self.tr7.price_includes_tax = False
-        self.tr7.save()
-        SubEventItem.objects.create(subevent=se2, item=self.ticket, price=10)
-        self.op1.subevent = se1
-        self.op1.save()
-        self.quota.subevent = se2
-        self.quota.save()
-
-        self.ocm.change_subevent(self.op1, se2)
-        self.ocm.commit()
-        self.op1.refresh_from_db()
-        self.order.refresh_from_db()
-        assert self.op1.subevent == se2
-        assert self.op1.price == Decimal('10.70')
         assert self.order.total == self.op1.price + self.op2.price
 
     def test_change_subevent_sold_out(self):
@@ -680,14 +658,14 @@ class OrderChangeManagerTests(TestCase):
 
     def test_change_item_keep_price(self):
         p = self.op1.price
-        tv = self.op1.tax_value
+        self.ocm.change_item(self.op1, self.shirt, None)
-        self.ocm.change_item(self.op1, self.shirt, None, keep_price=True)
         self.ocm.commit()
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
         assert self.op1.item == self.shirt
         assert self.op1.price == p
-        assert self.op1.tax_value == tv
+        assert self.op1.tax_value == Decimal('3.67')
+        assert self.op1.tax_rule == self.shirt.tax_rule
 
     def test_change_item_success(self):
         self.ocm.change_item(self.op1, self.shirt, None)
@@ -695,36 +673,23 @@ class OrderChangeManagerTests(TestCase):
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
         assert self.op1.item == self.shirt
-        assert self.op1.price == self.shirt.default_price
+        assert self.op1.price == Decimal('23.00')
         assert self.op1.tax_rate == self.shirt.tax_rule.rate
         assert round_decimal(self.op1.price * (1 - 100 / (100 + self.op1.tax_rate))) == self.op1.tax_value
         assert self.order.total == self.op1.price + self.op2.price
 
-    def test_change_item_net_price_success(self):
+    def test_change_item_with_price_success(self):
-        self.tr19.price_includes_tax = False
-        self.tr19.save()
         self.ocm.change_item(self.op1, self.shirt, None)
+        self.ocm.change_price(self.op1, Decimal('12.00'))
         self.ocm.commit()
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
         assert self.op1.item == self.shirt
-        assert self.op1.price == Decimal('14.28')
+        assert self.op1.price == Decimal('12.00')
         assert self.op1.tax_rate == self.shirt.tax_rule.rate
         assert round_decimal(self.op1.price * (1 - 100 / (100 + self.op1.tax_rate))) == self.op1.tax_value
         assert self.order.total == self.op1.price + self.op2.price
 
-    def test_change_item_reverse_charge(self):
-        self._enable_reverse_charge()
-        self.ocm.change_item(self.op1, self.shirt, None)
-        self.ocm.commit()
-        self.op1.refresh_from_db()
-        self.order.refresh_from_db()
-        assert self.op1.item == self.shirt
-        assert self.op1.price == Decimal('10.08')
-        assert self.op1.tax_rate == Decimal('0.00')
-        assert self.op1.tax_value == Decimal('0.00')
-        assert self.order.total == self.op1.price + self.op2.price
-
     def test_change_price_success(self):
         self.ocm.change_price(self.op1, Decimal('24.00'))
         self.ocm.commit()
@@ -738,7 +703,7 @@ class OrderChangeManagerTests(TestCase):
     def test_change_price_net_success(self):
         self.tr7.price_includes_tax = False
         self.tr7.save()
-        self.ocm.change_price(self.op1, Decimal('10.00'))
+        self.ocm.change_price(self.op1, Decimal('10.70'))
         self.ocm.commit()
         self.op1.refresh_from_db()
         self.order.refresh_from_db()

src/tests/control/test_orders.py

@@ -935,11 +935,9 @@ class OrderChangeTests(SoupTest):
         self.client.post('/control/event/{}/{}/orders/{}/change'.format(
             self.event.organizer.slug, self.event.slug, self.order.code
         ), {
-            'op-{}-operation'.format(self.op1.pk): 'product',
             'op-{}-itemvar'.format(self.op1.pk): str(self.shirt.pk),
-            'op-{}-operation'.format(self.op2.pk): '',
+            'op-{}-price'.format(self.op1.pk): str('12.00'),
-            'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),
+            'add-itemvar': str(self.ticket.pk),
-            'add-itemvar'.format(self.op2.pk): str(self.ticket.pk),
         })
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
@@ -965,14 +963,9 @@ class OrderChangeTests(SoupTest):
         self.client.post('/control/event/{}/{}/orders/{}/change'.format(
             self.event.organizer.slug, self.event.slug, self.order.code
         ), {
-            'op-{}-operation'.format(self.op1.pk): 'subevent',
             'op-{}-subevent'.format(self.op1.pk): str(se2.pk),
-            'op-{}-itemvar'.format(self.op1.pk): str(self.ticket.pk),
+            'add-itemvar': str(self.ticket.pk),
-            'op-{}-operation'.format(self.op2.pk): '',
+            'add-subevent': str(se1.pk),
-            'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),
-            'op-{}-subevent'.format(self.op2.pk): str(se1.pk),
-            'add-itemvar'.format(self.op2.pk): str(self.ticket.pk),
-            'add-subevent'.format(self.op2.pk): str(se1.pk),
         })
         self.op1.refresh_from_db()
         self.op2.refresh_from_db()
@@ -989,7 +982,7 @@ class OrderChangeTests(SoupTest):
             'op-{}-price'.format(self.op1.pk): '24.00',
             'op-{}-operation'.format(self.op2.pk): '',
             'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),
-            'add-itemvar'.format(self.op2.pk): str(self.ticket.pk),
+            'add-itemvar': str(self.ticket.pk),
         })
         self.op1.refresh_from_db()
         self.order.refresh_from_db()
@@ -1001,13 +994,8 @@ class OrderChangeTests(SoupTest):
         self.client.post('/control/event/{}/{}/orders/{}/change'.format(
             self.event.organizer.slug, self.event.slug, self.order.code
         ), {
-            'op-{}-operation'.format(self.op1.pk): 'cancel',
+            'op-{}-operation_cancel'.format(self.op1.pk): 'on',
-            'op-{}-itemvar'.format(self.op1.pk): str(self.ticket.pk),
+            'add-itemvar': str(self.ticket.pk),
-            'op-{}-price'.format(self.op1.pk): str(self.op1.price),
-            'op-{}-operation'.format(self.op2.pk): '',
-            'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),
-            'op-{}-price'.format(self.op2.pk): str(self.op2.price),
-            'add-itemvar'.format(self.op2.pk): str(self.ticket.pk),
         })
         self.order.refresh_from_db()
         assert self.order.positions.count() == 1
@@ -1017,12 +1005,6 @@ class OrderChangeTests(SoupTest):
         self.client.post('/control/event/{}/{}/orders/{}/change'.format(
             self.event.organizer.slug, self.event.slug, self.order.code
         ), {
-            'op-{}-operation'.format(self.op1.pk): '',
-            'op-{}-operation'.format(self.op2.pk): '',
-            'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),
-            'op-{}-price'.format(self.op2.pk): str(self.op2.price),
-            'op-{}-itemvar'.format(self.op1.pk): str(self.ticket.pk),
-            'op-{}-price'.format(self.op1.pk): str(self.op1.price),
             'add-itemvar': str(self.shirt.pk),
             'add-do': 'on',
             'add-price': '14.00',
@@ -1047,7 +1029,7 @@ class OrderChangeTests(SoupTest):
             self.event.organizer.slug, self.event.slug, self.order.code
         ), {
             'other-recalculate_taxes': 'on',
-            'add-itemvar'.format(self.op2.pk): str(self.ticket.pk),
+            'add-itemvar': str(self.ticket.pk),
             'op-{}-operation'.format(self.op1.pk): '',
             'op-{}-operation'.format(self.op2.pk): '',
             'op-{}-itemvar'.format(self.op2.pk): str(self.ticket.pk),