Added support for the to_field on ForeignKey Fields.

Uses the SlugRelatedField instead.

SlugRelatedField will only get the Slugfield from the ORM as it does not need the other stuff

rest_framework/relations.py

@@ -303,7 +303,7 @@ class SlugRelatedField(RelatedField):
 
     def to_internal_value(self, data):
         try:
-            return self.get_queryset().get(**{self.slug_field: data})
+            return self.get_queryset().only(self.slug_field).get(**{self.slug_field: data})
         except ObjectDoesNotExist:
             self.fail('does_not_exist', slug_name=self.slug_field, value=smart_text(data))
         except (TypeError, ValueError):

rest_framework/serializers.py

@@ -727,6 +727,7 @@ class ModelSerializer(Serializer):
         models.URLField: URLField,
     })
     _related_class = PrimaryKeyRelatedField
+    _related_to_field_class = SlugRelatedField
 
     def create(self, validated_data):
         """
@@ -1002,8 +1003,15 @@ class ModelSerializer(Serializer):
                     field_cls = self._get_nested_class(depth, relation_info)
                     kwargs = get_nested_relation_kwargs(relation_info)
                 else:
-                    field_cls = self._related_class
                     kwargs = get_relation_kwargs(field_name, relation_info)
+                    to_field = kwargs.get('to_field', False)
+                    if to_field:
+                        # using the slug field for now
+                        kwargs.pop('to_field', None)
+                        kwargs['slug_field'] = to_field
+                        field_cls = self._related_to_field_class
+                    else:
+                        field_cls = self._related_class
                     # `view_name` is only valid for hyperlinked relationships.
                     if not issubclass(field_cls, HyperlinkedRelatedField):
                         kwargs.pop('view_name', None)

rest_framework/utils/field_mapping.py

@@ -194,7 +194,7 @@ def get_relation_kwargs(field_name, relation_info):
     """
     Creates a default instance of a flat relational field.
     """
-    model_field, related_model, to_many, has_through_model = relation_info
+    model_field, related_model, to_many, to_field, has_through_model = relation_info
     kwargs = {
         'queryset': related_model._default_manager,
         'view_name': get_detail_view_name(related_model)
@@ -203,6 +203,9 @@ def get_relation_kwargs(field_name, relation_info):
     if to_many:
         kwargs['many'] = True
 
+    if to_field:
+        kwargs['to_field'] = to_field
+
     if has_through_model:
         kwargs['read_only'] = True
         kwargs.pop('queryset', None)

rest_framework/utils/model_meta.py

@@ -26,6 +26,7 @@ RelationInfo = namedtuple('RelationInfo', [
     'model_field',
     'related',
     'to_many',
+    'to_field',
     'has_through_model'
 ])
 
@@ -96,10 +97,13 @@ def _get_forward_relationships(opts):
     """
     forward_relations = OrderedDict()
     for field in [field for field in opts.fields if field.serialize and field.rel]:
+
         forward_relations[field.name] = RelationInfo(
             model_field=field,
             related=_resolve_model(field.rel.to),
             to_many=False,
+            # to_fields is an array but django lets you only set one to_field
+            to_field=field.to_fields[0] if len(field.to_fields) else None,
             has_through_model=False
         )
 
@@ -109,6 +113,8 @@ def _get_forward_relationships(opts):
             model_field=field,
             related=_resolve_model(field.rel.to),
             to_many=True,
+            # to_fields is an array but django lets you only set one to_field
+            to_field=field.to_fields[0] if len(field.to_fields) else None,
             has_through_model=(
                 not field.rel.through._meta.auto_created
             )