Fix unique_together validation with source (#9482)

rest_framework/validators.py

@@ -159,17 +159,18 @@ class UniqueTogetherValidator:
         queryset = self.filter_queryset(attrs, queryset, serializer)
         queryset = self.exclude_current_instance(attrs, queryset, serializer.instance)
 
+        checked_names = [
+            serializer.fields[field_name].source for field_name in self.fields
+        ]
         # Ignore validation if any field is None
         if serializer.instance is None:
-            checked_values = [
-                value for field, value in attrs.items() if field in self.fields
-            ]
+            checked_values = [attrs[field_name] for field_name in checked_names]
         else:
             # Ignore validation if all field values are unchanged
             checked_values = [
-                value
-                for field, value in attrs.items()
-                if field in self.fields and value != getattr(serializer.instance, field)
+                attrs[field_name]
+                for field_name in checked_names
+                if attrs[field_name] != getattr(serializer.instance, field_name)
             ]
 
         if checked_values and None not in checked_values and qs_exists(queryset):

tests/test_validators.py

@@ -469,6 +469,28 @@ class TestUniquenessTogetherValidation(TestCase):
             assert serializer.is_valid()
             assert not mock.called
 
+    @patch("rest_framework.validators.qs_exists")
+    def test_unique_together_with_source(self, mock_qs_exists):
+        class UniqueTogetherWithSourceSerializer(serializers.ModelSerializer):
+            name = serializers.CharField(source="race_name")
+            pos = serializers.IntegerField(source="position")
+
+            class Meta:
+                model = UniquenessTogetherModel
+                fields = ["name", "pos"]
+
+        data = {"name": "Paris Marathon", "pos": 1}
+        instance = UniquenessTogetherModel.objects.create(
+            race_name="Paris Marathon", position=1
+        )
+        serializer = UniqueTogetherWithSourceSerializer(data=data)
+        assert not serializer.is_valid()
+        assert mock_qs_exists.called
+        mock_qs_exists.reset_mock()
+        serializer = UniqueTogetherWithSourceSerializer(data=data, instance=instance)
+        assert serializer.is_valid()
+        assert not mock_qs_exists.called
+
     def test_filter_queryset_do_not_skip_existing_attribute(self):
         """
         filter_queryset should add value from existing instance attribute