Add ability works with links in Relation ship.

jsonapi_requests/orm/fields.py

@@ -124,7 +124,14 @@ def get_object_key(self):
         except KeyError:
             raise ObjectKeyError
         else:
-            data = relationship.data
+            data = None
+            if (hasattr(relationship, 'data') and relationship.data.as_data() != {}) or relationship.as_data() == {}:
+                data = relationship.data
+            elif hasattr(relationship, 'links') and relationship.links != {}:
+                res = self.instance._options.api.endpoint(path=relationship.links.as_data()['self'])
+                relationship_data = res.get()
+                data = relationship_data.data
+
             if data.type is None or data.id is None:
                 raise ObjectKeyError
             else:

jsonapi_requests/request_factory.py

@@ -36,8 +36,8 @@ def request(self, api_path, method, *, object: data.JsonApiObject=None, **kwargs
     @property
     def retrying(self):
         retry_condition = (
-            tenacity.retry_if_exception_type(ApiConnectionError)
-            | tenacity.retry_if_exception_type(ApiInternalServerError)
+            tenacity.retry_if_exception_type(ApiConnectionError) |
+            tenacity.retry_if_exception_type(ApiInternalServerError)
         )
         return tenacity.Retrying(
             reraise=True,

tests/test_orm.py

@@ -106,6 +106,30 @@ class Meta:
         test = Test.from_response_content(response_content)
         assert test.other is None
 
+    def test_from_response_with_relationship_with_links_only(self):
+        mock_api = mock.MagicMock()
+        mock_api.endpoint().get().data = data.ResourceIdentifier(type='test', id='159')
+        response_content = data.JsonApiResponse(
+            data=data.JsonApiObject(id='1', type='test', relationships={
+                'other': data.Relationship(links=data.Dictionary(self='http://example.org/api/rest/test/1/relationships'
+                                                                      '/vendor',
+                                                                 related='http://example.org/api/rest/test/1/vendor'
+                                                                 )
+                                           )
+            })
+        )
+        orm_api = orm.OrmApi(mock_api)
+
+        class Test(orm.ApiModel):
+            class Meta:
+                api = orm_api
+                type = 'test'
+            other = orm.RelationField(source='other')
+            name = orm.AttributeField(source='name')
+        test = Test.from_response_content(response_content)
+        assert test.other.type is 'test'
+        assert test.other.id is '159'
+
     def test_issue_19_attributes_are_readable_with_multiple_relations(self):
         response_content = data.JsonApiResponse(
             data=data.JsonApiObject(