Extract type for each related instance

Instead of extracting the resource type for the whole related
collection, extract the type for each instance individually. This way,
polymorphic relationships (using something like django_polymorphic) are
supported.

Author: martinmaillard

rest_framework_json_api/utils.py

@@ -164,7 +164,9 @@ def build_json_resource_obj(fields, resource, resource_instance, resource_name):
 
 
 def get_related_resource_type(relation):
-    if hasattr(relation, 'get_queryset') and relation.get_queryset() is not None:
+    if hasattr(relation, '_meta'):
+        relation_model = relation._meta.model
+    elif hasattr(relation, 'get_queryset') and relation.get_queryset() is not None:
         relation_model = relation.get_queryset().model
     else:
         parent_serializer = relation.parent
@@ -266,11 +268,10 @@ def extract_relationships(fields, resource, resource_instance):
 
         if isinstance(field, ManyRelatedField):
             relation_data = list()
-            related_object = field.child_relation
-            relation_type = get_related_resource_type(related_object)
             for related_object in relation_instance_or_manager.all():
+                related_object_type = get_related_resource_type(related_object)
                 relation_data.append(OrderedDict([
-                    ('type', relation_type),
+                    ('type', related_object_type),
                     ('id', encoding.force_text(related_object.pk))
                 ]))
             data.update({
@@ -285,20 +286,18 @@ def extract_relationships(fields, resource, resource_instance):
 
         if isinstance(field, ListSerializer):
             relation_data = list()
-            serializer = field.child
-            relation_model = serializer.Meta.model
-            relation_type = format_relation_name(relation_model.__name__)
 
             serializer_data = resource.get(field_name)
             resource_instance_queryset = relation_instance_or_manager.all()
             if isinstance(serializer_data, list):
                 for position in range(len(serializer_data)):
                     nested_resource_instance = resource_instance_queryset[position]
-                    relation_data.append(
-                        OrderedDict(
-                            [('type', relation_type), ('id', encoding.force_text(nested_resource_instance.pk))]
-                        )
-                    )
+                    nested_resource_instance_type = get_related_resource_type(
+                        nested_resource_instance)
+                    relation_data.append(OrderedDict([
+                        ('type', nested_resource_instance_type),
+                        ('id', encoding.force_text(nested_resource_instance.pk))
+                    ]))
 
                 data.update({field_name: {'data': relation_data}})
                 continue