Fix UniqueTogetherValidator with field sources (#7086)

* Add failing tests for unique_together+source

* Fix UniqueTogetherValidator source handling

* Fix read-only+default+source handling

* Update test to use functional serializer

* Test UniqueTogetherValidator error+source

rest_framework/serializers.py

@@ -448,7 +448,7 @@ class Serializer(BaseSerializer, metaclass=SerializerMetaclass):
                 default = field.get_default()
             except SkipField:
                 continue
-            defaults[field.field_name] = default
+            defaults[field.source] = default
 
         return defaults
 

rest_framework/validators.py

@@ -106,7 +106,7 @@ class UniqueTogetherValidator:
         missing_items = {
             field_name: self.missing_message
             for field_name in self.fields
-            if field_name not in attrs
+            if serializer.fields[field_name].source not in attrs
         }
         if missing_items:
             raise ValidationError(missing_items, code='required')
@@ -115,17 +115,23 @@ class UniqueTogetherValidator:
         """
         Filter the queryset to all instances matching the given attributes.
         """
+        # field names => field sources
+        sources = [
+            serializer.fields[field_name].source
+            for field_name in self.fields
+        ]
+
         # If this is an update, then any unprovided field should
         # have it's value set based on the existing instance attribute.
         if serializer.instance is not None:
-            for field_name in self.fields:
-                if field_name not in attrs:
-                    attrs[field_name] = getattr(serializer.instance, field_name)
+            for source in sources:
+                if source not in attrs:
+                    attrs[source] = getattr(serializer.instance, source)
 
         # Determine the filter keyword arguments and filter the queryset.
         filter_kwargs = {
-            field_name: attrs[field_name]
-            for field_name in self.fields
+            source: attrs[source]
+            for source in sources
         }
         return qs_filter(queryset, **filter_kwargs)
 

tests/test_validators.py

@@ -301,6 +301,49 @@ class TestUniquenessTogetherValidation(TestCase):
             ]
         }
 
+    def test_read_only_fields_with_default_and_source(self):
+        class ReadOnlySerializer(serializers.ModelSerializer):
+            name = serializers.CharField(source='race_name', default='test', read_only=True)
+
+            class Meta:
+                model = UniquenessTogetherModel
+                fields = ['name', 'position']
+                validators = [
+                    UniqueTogetherValidator(
+                        queryset=UniquenessTogetherModel.objects.all(),
+                        fields=['name', 'position']
+                    )
+                ]
+
+        serializer = ReadOnlySerializer(data={'position': 1})
+        assert serializer.is_valid(raise_exception=True)
+
+    def test_writeable_fields_with_source(self):
+        class WriteableSerializer(serializers.ModelSerializer):
+            name = serializers.CharField(source='race_name')
+
+            class Meta:
+                model = UniquenessTogetherModel
+                fields = ['name', 'position']
+                validators = [
+                    UniqueTogetherValidator(
+                        queryset=UniquenessTogetherModel.objects.all(),
+                        fields=['name', 'position']
+                    )
+                ]
+
+        serializer = WriteableSerializer(data={'name': 'test', 'position': 1})
+        assert serializer.is_valid(raise_exception=True)
+
+        # Validation error should use seriazlier field name, not source
+        serializer = WriteableSerializer(data={'position': 1})
+        assert not serializer.is_valid()
+        assert serializer.errors == {
+            'name': [
+                'This field is required.'
+            ]
+        }
+
     def test_allow_explict_override(self):
         """
         Ensure validators can be explicitly removed..
@@ -357,13 +400,9 @@ class TestUniquenessTogetherValidation(TestCase):
             def filter(self, **kwargs):
                 self.called_with = kwargs
 
-        class MockSerializer:
-            def __init__(self, instance):
-                self.instance = instance
-
         data = {'race_name': 'bar'}
         queryset = MockQueryset()
-        serializer = MockSerializer(instance=self.instance)
+        serializer = UniquenessTogetherSerializer(instance=self.instance)
         validator = UniqueTogetherValidator(queryset, fields=('race_name',
                                                               'position'))
         validator.filter_queryset(attrs=data, queryset=queryset, serializer=serializer)