New implementation of sales channels (#4111)

Co-authored-by: Martin Gross <gross@rami.io>

src/pretix/api/serializers/cart.py

@@ -33,7 +33,7 @@ from pretix.api.serializers.i18n import I18nAwareModelSerializer
 from pretix.api.serializers.order import (
     AnswerCreateSerializer, AnswerSerializer, InlineSeatSerializer,
 )
-from pretix.base.models import Seat, Voucher
+from pretix.base.models import SalesChannel, Seat, Voucher
 from pretix.base.models.orders import CartPosition
 
 
@@ -212,7 +212,11 @@ class CartPositionCreateSerializer(BaseCartPositionCreateSerializer):
     addons = BaseCartPositionCreateSerializer(many=True, required=False)
     bundled = BaseCartPositionCreateSerializer(many=True, required=False)
     seat = serializers.CharField(required=False, allow_null=True)
-    sales_channel = serializers.CharField(required=False, default='sales_channel')
+    sales_channel = serializers.SlugRelatedField(
+        slug_field='identifier',
+        queryset=SalesChannel.objects.none(),
+        required=False,
+    )
     voucher = serializers.CharField(required=False, allow_null=True)
 
     class Meta:
@@ -221,6 +225,10 @@ class CartPositionCreateSerializer(BaseCartPositionCreateSerializer):
             'cart_id', 'expires', 'addons', 'bundled', 'seat', 'sales_channel', 'voucher'
         )
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields["sales_channel"].queryset = self.context["event"].organizer.sales_channels.all()
+
     def validate_cart_id(self, cid):
         if cid and not cid.endswith('@api'):
             raise ValidationError('Cart ID should end in @api or be empty.')