Merge pull request #96 from datapane/fix/drf-311-validators

Update UniqueFieldsMixin to support DRF 3.11 validator context API

drf_writable_nested/mixins.py

@@ -400,10 +400,13 @@ def get_fields(self):
     def _validate_unique_fields(self, validated_data):
         for field_name in self._unique_fields:
             unique_validator = UniqueValidator(self.Meta.model.objects.all())
-            unique_validator.set_context(self.fields[field_name])
-
             try:
-                unique_validator(validated_data[field_name])
+                # `set_context` removed on DRF >= 3.11, pass in via __call__ instead
+                if hasattr(unique_validator, 'set_context'):
+                    unique_validator.set_context(self.fields[field_name])
+                    unique_validator(validated_data[field_name])
+                else:
+                    unique_validator(validated_data[field_name], self.fields[field_name])
             except ValidationError as exc:
                 raise ValidationError({field_name: exc.detail})