Allow to add positions to an existing order

src/pretix/control/forms/orders.py

@@ -7,7 +7,7 @@ from django.utils.timezone import now
 from django.utils.translation import ugettext_lazy as _
 
 from pretix.base.forms import I18nModelForm
-from pretix.base.models import Item, Order
+from pretix.base.models import Item, ItemAddOn, Order, OrderPosition
 
 
 class ExtendForm(I18nModelForm):
@@ -55,6 +55,52 @@ class CommentForm(I18nModelForm):
         }
 
 
+class OrderPositionAddForm(forms.Form):
+    do = forms.BooleanField(
+        label=_('Add a new product to the order'),
+        required=False
+    )
+    itemvar = forms.ChoiceField(
+        label=_('Product')
+    )
+    addon_to = forms.ModelChoiceField(
+        OrderPosition.objects.none(),
+        required=False,
+        label=_('Add-on to'),
+    )
+    price = forms.DecimalField(
+        required=False,
+        max_digits=10, decimal_places=2,
+        label=_('Gross price'),
+        help_text=_("Keep empty for the product's default price")
+    )
+
+    def __init__(self, *args, **kwargs):
+        order = kwargs.pop('order')
+        super().__init__(*args, **kwargs)
+        choices = []
+        for i in order.event.items.prefetch_related('variations').all():
+            pname = str(i.name)
+            if not i.is_available():
+                pname += ' ({})'.format(_('inactive'))
+            variations = list(i.variations.all())
+            if variations:
+                for v in variations:
+                    choices.append(('%d-%d' % (i.pk, v.pk),
+                                    '%s – %s (%s %s)' % (pname, v.value, localize(v.price),
+                                                         order.event.currency)))
+            else:
+                choices.append((str(i.pk), '%s (%s %s)' % (pname, localize(i.default_price),
+                                                           order.event.currency)))
+        self.fields['itemvar'].choices = choices
+        if ItemAddOn.objects.filter(base_item__event=order.event).exists():
+            self.fields['addon_to'].queryset = order.positions.filter(addon_to__isnull=True).select_related(
+                'item', 'variation'
+            )
+        else:
+            del self.fields['addon_to']
+
+
 class OrderPositionChangeForm(forms.Form):
     itemvar = forms.ChoiceField()
     price = forms.DecimalField(

src/pretix/control/logdisplay.py

@@ -6,7 +6,7 @@ from django.utils import formats
 from django.utils.translation import ugettext_lazy as _
 from i18nfield.strings import LazyI18nString
 
-from pretix.base.models import Event, ItemVariation, LogEntry
+from pretix.base.models import Event, ItemVariation, LogEntry, OrderPosition
 from pretix.base.signals import logentry_display
 
 OVERVIEW_BLACKLIST = [
@@ -51,6 +51,26 @@ def _display_order_changed(event: Event, logentry: LogEntry):
             old_price=formats.localize(Decimal(data['old_price'])),
             currency=event.currency
         )
+    elif logentry.action_type == 'pretix.event.order.changed.add':
+        item = str(event.items.get(pk=data['item']))
+        if data['variation']:
+            item += ' - ' + str(ItemVariation.objects.get(item__event=event, pk=data['variation']))
+        if data['addon_to']:
+            addon_to = OrderPosition.objects.get(order__event=event, pk=data['addon_to'])
+            return text + ' ' + _('Position #{posid} created: {item} ({price} {currency}) as an add-on to '
+                                  'position #{addon_to}.').format(
+                posid=data.get('positionid', '?'),
+                item=item, addon_to=addon_to.positionid,
+                price=formats.localize(Decimal(data['price'])),
+                currency=event.currency
+            )
+        else:
+            return text + ' ' + _('Position #{posid} created: {item} ({price} {currency}).').format(
+                posid=data.get('positionid', '?'),
+                item=item,
+                price=formats.localize(Decimal(data['price'])),
+                currency=event.currency
+            )
 
 
 @receiver(signal=logentry_display, dispatch_uid="pretixcontrol_logentry_display")

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

@@ -22,8 +22,7 @@
     <p>
         {% blocktrans trimmed %}
             The user will receive a notification about the change but in the case of new required questions, the user
-            will not be forced to answer them. You cannot use this form to add something to the order, please create
-            a second order instead.
+            will not be forced to answer them.
         {% endblocktrans %}
     </p>
     <p>
@@ -31,13 +30,15 @@
             If an invoice is attached to the order, a cancellation will be created together with a new invoice.
         {% endblocktrans %}
     </p>
-    <div class="alert alert-warning">
+    <div class="alert alert-warning"><strong>
         {% blocktrans trimmed %}
-            Please use this tool carefully. Changes you make here are not reversible. In most cases it is easier to
-            cancel the order completely and create a new one.
+            Please use this tool carefully. Changes you make here are not reversible. Also, if you change an order
+            manually, not all constraints (e.g. on required add-ons) will be checked. Therefore, you might construct
+            an order that would not be able to exist otherwise.
+            In most cases it is easier to cancel the order completely and create a new one.
         {% endblocktrans %}
-    </div>
-    <form method="post" class="form-horizontal" href="">
+    </strong></div>
+    <form method="post" href="">
         {% csrf_token %}
         {% for position in positions %}
             <div class="panel panel-default items">
@@ -107,6 +108,29 @@
                 </div>
             </div>
         {% endfor %}
+        <div class="panel panel-default items">
+            <div class="panel-heading">
+                <h3 class="panel-title">
+                    Add product
+                </h3>
+            </div>
+            <div class="panel-body">
+                <div class="form-horizontal">
+                    {% bootstrap_form_errors add_form %}
+                    {% if add_form.custom_error %}
+                        <div class="alert alert-danger">
+                            {{ add_form.custom_error }}
+                        </div>
+                    {% endif %}
+                    {% bootstrap_field add_form.do layout='horizontal' %}
+                    {% bootstrap_field add_form.itemvar layout='horizontal' %}
+                    {% bootstrap_field add_form.price layout='horizontal' %}
+                    {% if add_form.addon_to %}
+                        {% bootstrap_field add_form.addon_to layout='horizontal' %}
+                    {% endif %}
+                </div>
+            </div>
+        </div>
         <div class="form-group submit-group">
             <a class="btn btn-default btn-lg"
                     href="{% url "control:event.order" event=request.event.slug organizer=request.event.organizer.slug code=order.code %}">

src/pretix/control/views/orders.py

@@ -33,7 +33,7 @@ from pretix.base.signals import (
 from pretix.base.views.async import AsyncAction
 from pretix.control.forms.orders import (
     CommentForm, ExporterForm, ExtendForm, OrderContactForm, OrderLocaleForm,
-    OrderPositionChangeForm,
+    OrderPositionAddForm, OrderPositionChangeForm,
 )
 from pretix.control.permissions import EventPermissionRequiredMixin
 from pretix.multidomain.urlreverse import build_absolute_uri
@@ -166,7 +166,7 @@ class OrderDetail(OrderView):
         cartpos = queryset.order_by(
             'item', 'variation'
         ).select_related(
-            'item', 'variation'
+            'item', 'variation', 'addon_to'
         ).prefetch_related(
             'item__questions', 'answers', 'answers__question', 'checkins'
         ).order_by('positionid')
@@ -181,6 +181,8 @@ class OrderDetail(OrderView):
             p.cache_answers()
             positions.append(p)
 
+        positions.sort(key=lambda p: p.sort_key)
+
         return {
             'positions': positions,
             'raw': cartpos,
@@ -460,6 +462,11 @@ class OrderChange(OrderView):
             return self._redirect_back()
         return super().dispatch(request, *args, **kwargs)
 
+    @cached_property
+    def add_form(self):
+        return OrderPositionAddForm(prefix='add', order=self.order,
+                                    data=self.request.POST if self.request.method == "POST" else None)
+
     @cached_property
     def positions(self):
         positions = list(self.order.positions.all())
@@ -471,15 +478,37 @@ class OrderChange(OrderView):
     def get_context_data(self, **kwargs):
         ctx = super().get_context_data(**kwargs)
         ctx['positions'] = self.positions
+        ctx['add_form'] = self.add_form
         return ctx
 
-    def post(self, *args, **kwargs):
-        ocm = OrderChangeManager(self.order, self.request.user)
-        form_valid = True
+    def _process_add(self, ocm):
+        if not self.add_form.is_valid():
+            return False
+        else:
+            if self.add_form.cleaned_data['do']:
+                if '-' in self.add_form.cleaned_data['itemvar']:
+                    itemid, varid = self.add_form.cleaned_data['itemvar'].split('-')
+                else:
+                    itemid, varid = self.add_form.cleaned_data['itemvar'], None
+
+                item = Item.objects.get(pk=itemid, event=self.request.event)
+                if varid:
+                    variation = ItemVariation.objects.get(pk=varid, item=item)
+                else:
+                    variation = None
+                try:
+                    ocm.add_position(item, variation,
+                                     self.add_form.cleaned_data['price'],
+                                     self.add_form.cleaned_data['addon_to'])
+                except OrderError as e:
+                    self.add_form.custom_error = str(e)
+                    return False
+        return True
+
+    def _process_change(self, ocm):
         for p in self.positions:
             if not p.form.is_valid():
-                form_valid = False
-                break
+                return False
 
             try:
                 if p.form.cleaned_data['operation'] == 'product':
@@ -501,8 +530,12 @@ class OrderChange(OrderView):
 
             except OrderError as e:
                 p.custom_error = str(e)
-                form_valid = False
-                break
+                return False
+        return True
+
+    def post(self, *args, **kwargs):
+        ocm = OrderChangeManager(self.order, self.request.user)
+        form_valid = self._process_add(ocm) and self._process_change(ocm)
 
         if not form_valid:
             messages.error(self.request, _('An error occured. Please see the details below.'))