Added support for the to_field on ForeignKey fields

rest_framework/serializers.py

@@ -794,6 +794,7 @@ class ModelSerializer(Serializer):
     if ModelJSONField is not None:
         serializer_field_mapping[ModelJSONField] = JSONField
     serializer_related_field = PrimaryKeyRelatedField
+    serializer_related_to_field = SlugRelatedField
     serializer_url_field = HyperlinkedIdentityField
     serializer_choice_field = ChoiceField
 
@@ -1129,6 +1130,11 @@ class ModelSerializer(Serializer):
         field_class = self.serializer_related_field
         field_kwargs = get_relation_kwargs(field_name, relation_info)
 
+        to_field = field_kwargs.pop('to_field', None)
+        if to_field and to_field != 'id':
+            field_kwargs['slug_field'] = to_field
+            field_class = self.serializer_related_to_field
+
         # `view_name` is only valid for hyperlinked relationships.
         if not issubclass(field_class, HyperlinkedRelatedField):
             field_kwargs.pop('view_name', None)

rest_framework/utils/field_mapping.py

@@ -222,7 +222,7 @@ 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)
@@ -231,6 +231,9 @@ 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_model',
     'to_many',
+    'to_field',
     'has_through_model'
 ])
 
@@ -90,6 +91,10 @@ def _get_fields(opts):
     return fields
 
 
+def _get_to_field(field):
+    return field.to_fields[0] if field.to_fields else None
+
+
 def _get_forward_relationships(opts):
     """
     Returns an `OrderedDict` of field names to `RelationInfo`.
@@ -100,6 +105,7 @@ def _get_forward_relationships(opts):
             model_field=field,
             related_model=_resolve_model(field.rel.to),
             to_many=False,
+            to_field=_get_to_field(field),
             has_through_model=False
         )
 
@@ -109,6 +115,8 @@ def _get_forward_relationships(opts):
             model_field=field,
             related_model=_resolve_model(field.rel.to),
             to_many=True,
+            # manytomany do not have to_fields
+            to_field=None,
             has_through_model=(
                 not field.rel.through._meta.auto_created
             )
@@ -133,6 +141,7 @@ def _get_reverse_relationships(opts):
             model_field=None,
             related_model=related,
             to_many=relation.field.rel.multiple,
+            to_field=_get_to_field(relation.field),
             has_through_model=False
         )
 
@@ -144,6 +153,8 @@ def _get_reverse_relationships(opts):
             model_field=None,
             related_model=related,
             to_many=True,
+            # manytomany do not have to_fields
+            to_field=None,
             has_through_model=(
                 (getattr(relation.field.rel, 'through', None) is not None) and
                 not relation.field.rel.through._meta.auto_created