Add sales channels (#1103)

- [x] Data model
- [x] Enforce constraint
- [x] Filter order list
- [x] Set channel on created order
- [x] Products API
- [x] Order API
- [x] Tests
- [x] Filter reports
- [x] Resellers
- [ ] deploy plugins
  - [ ] posbackend
  - [ ] resellers
  - [ ] reports
- [x] Ticketlayouts
- [x] Support in pretixPOS

src/pretix/base/models/fields.py

@@ -0,0 +1,94 @@
+from django.core import exceptions
+from django.db.models import TextField, lookups as builtin_lookups
+from django.utils.translation import gettext_lazy as _
+from rest_framework import serializers
+from rest_framework.exceptions import ValidationError
+
+DELIMITER = "\x1F"
+
+
+class MultiStringField(TextField):
+    default_error_messages = {
+        'delimiter_found': _('No value can contain the delimiter character.')
+    }
+
+    def __init__(self, verbose_name=None, name=None, **kwargs):
+        super().__init__(verbose_name, name, **kwargs)
+
+    def deconstruct(self):
+        name, path, args, kwargs = super().deconstruct()
+        return name, path, args, kwargs
+
+    def to_python(self, value):
+        if isinstance(value, (list, tuple)):
+            return value
+        elif value:
+            return [v for v in value.split(DELIMITER) if v]
+        else:
+            return []
+
+    def get_prep_value(self, value):
+        if isinstance(value, (list, tuple)):
+            return DELIMITER + DELIMITER.join(value) + DELIMITER
+        elif value is None:
+            return ""
+        raise TypeError("Invalid data type passed.")
+
+    def get_prep_lookup(self, lookup_type, value):  # NOQA
+        raise TypeError('Lookups on multi strings are currently not supported.')
+
+    def from_db_value(self, value, expression, connection, context):
+        if value:
+            return [v for v in value.split(DELIMITER) if v]
+        else:
+            return []
+
+    def validate(self, value, model_instance):
+        super().validate(value, model_instance)
+        for l in value:
+            if DELIMITER in l:
+                raise exceptions.ValidationError(
+                    self.error_messages['delimiter_found'],
+                    code='delimiter_found',
+                )
+
+    def get_lookup(self, lookup_name):
+        if lookup_name == 'contains':
+            return MultiStringContains
+        elif lookup_name == 'icontains':
+            return MultiStringIContains
+        raise NotImplementedError(
+            "Lookup '{}' doesn't work with MultiStringField".format(lookup_name),
+        )
+
+
+class MultiStringContains(builtin_lookups.Contains):
+    def process_rhs(self, qn, connection):
+        sql, params = super().process_rhs(qn, connection)
+        params[0] = "%" + DELIMITER + params[0][1:-1] + DELIMITER + "%"
+        return sql, params
+
+
+class MultiStringIContains(builtin_lookups.IContains):
+    def process_rhs(self, qn, connection):
+        sql, params = super().process_rhs(qn, connection)
+        params[0] = "%" + DELIMITER + params[0][1:-1] + DELIMITER + "%"
+        return sql, params
+
+
+class MultiStringSerializer(serializers.Field):
+    def __init__(self, **kwargs):
+        self.allow_blank = kwargs.pop('allow_blank', False)
+        super().__init__(**kwargs)
+
+    def to_representation(self, value):
+        return value
+
+    def to_internal_value(self, data):
+        if isinstance(data, list):
+            return data
+        else:
+            raise ValidationError('Invalid data type.')
+
+
+serializers.ModelSerializer.serializer_field_mapping[MultiStringField] = MultiStringSerializer