"Data" key optional in relationships

Author: Anton-Shutik

rest_framework_json_api/relations.py

@@ -7,8 +7,8 @@
 from django.core.exceptions import ImproperlyConfigured
 from django.urls import NoReverseMatch
 from django.utils.translation import ugettext_lazy as _
-from rest_framework.fields import MISSING_ERROR_MESSAGE
-from rest_framework.relations import MANY_RELATION_KWARGS, PrimaryKeyRelatedField
+from rest_framework.fields import MISSING_ERROR_MESSAGE, SkipField
+from rest_framework.relations import MANY_RELATION_KWARGS, PrimaryKeyRelatedField, ManyRelatedField as DRFManyRelatedField
 from rest_framework.reverse import reverse
 from rest_framework.serializers import Serializer
 
@@ -29,6 +29,21 @@
 ]
 
 
+class ManyRelatedField(DRFManyRelatedField):
+    '''
+    This workaround skips "data" rendering for relationships in order to save some sql queries and improve performance
+    '''
+
+    def __init__(self, child_relation=None, *args, **kwargs):
+        self.render_data = kwargs.pop('render_data', True)
+        super(ManyRelatedField, self).__init__(child_relation, *args, **kwargs)
+
+    def get_attribute(self, instance):
+        if self.render_data:
+            return super(ManyRelatedField, self).get_attribute(instance)
+        raise SkipField
+
+
 class ResourceRelatedField(PrimaryKeyRelatedField):
     _skip_polymorphic_optimization = True
     self_link_view_name = None
@@ -49,7 +64,7 @@ class ResourceRelatedField(PrimaryKeyRelatedField):
         'no_match': _('Invalid hyperlink - No URL match.'),
     }
 
-    def __init__(self, self_link_view_name=None, related_link_view_name=None, **kwargs):
+    def __init__(self, self_link_view_name=None, related_link_view_name=None, render_data=True, **kwargs):
         if self_link_view_name is not None:
             self.self_link_view_name = self_link_view_name
         if related_link_view_name is not None:
@@ -74,6 +89,29 @@ def __init__(self, self_link_view_name=None, related_link_view_name=None, **kwar
 
         super(ResourceRelatedField, self).__init__(**kwargs)
 
+    @classmethod
+    def many_init(cls, *args, **kwargs):
+        """
+        This method handles creating a parent `ManyRelatedField` instance
+        when the `many=True` keyword argument is passed.
+
+        Typically you won't need to override this method.
+
+        Note that we're over-cautious in passing most arguments to both parent
+        and child classes in order to try to cover the general case. If you're
+        overriding this method you'll probably want something much simpler, eg:
+
+        @classmethod
+        def many_init(cls, *args, **kwargs):
+            kwargs['child'] = cls()
+            return CustomManyRelatedField(*args, **kwargs)
+        """
+        list_kwargs = {'child_relation': cls(*args, **kwargs)}
+        for key in kwargs.keys():
+            if key in MANY_RELATION_KWARGS + ('render_data',):
+                list_kwargs[key] = kwargs[key]
+        return ManyRelatedField(**list_kwargs)
+
     def use_pk_only_optimization(self):
         # We need the real object to determine its type...
         return self.get_resource_type_from_included_serializer() is not None
@@ -293,7 +331,8 @@ def __new__(cls, *args, **kwargs):
             return cls.many_init(*args, **kwargs)
         return super(ResourceRelatedField, cls).__new__(cls, *args, **kwargs)
 
-    def __init__(self, child_relation=None, *args, **kwargs):
+    def __init__(self, child_relation=None, render_data=True, *args, **kwargs):
+        self.render_data = render_data
         model = kwargs.pop('model', None)
         if child_relation is not None:
             self.child_relation = child_relation
@@ -306,11 +345,13 @@ def many_init(cls, *args, **kwargs):
         list_kwargs = {k: kwargs.pop(k) for k in LINKS_PARAMS if k in kwargs}
         list_kwargs['child_relation'] = cls(*args, **kwargs)
         for key in kwargs.keys():
-            if key in ('model',) + MANY_RELATION_KWARGS:
+            if key in ('model', 'render_data') + MANY_RELATION_KWARGS:
                 list_kwargs[key] = kwargs[key]
         return cls(**list_kwargs)
 
     def get_attribute(self, instance):
+        if not self.render_data:
+            raise SkipField
         # check for a source fn defined on the serializer instead of the model
         if self.source and hasattr(self.parent, self.source):
             serializer_method = getattr(self.parent, self.source)

rest_framework_json_api/renderers.py

@@ -134,10 +134,12 @@ def extract_relationships(cls, fields, resource, resource_instance):
                     if not resolved:
                         continue
 
+                relation_data = {}
                 # special case for ResourceRelatedField
-                relation_data = {
-                    'data': resource.get(field_name)
-                }
+                if field_name in resource:
+                    relation_data.update({
+                        'data': resource.get(field_name)
+                    })
 
                 field_links = field.get_links(
                     resource_instance, field.related_link_lookup_field)
@@ -188,9 +190,15 @@ def extract_relationships(cls, fields, resource, resource_instance):
 
                 if isinstance(field.child_relation, ResourceRelatedField):
                     # special case for ResourceRelatedField
-                    relation_data = {
-                        'data': resource.get(field_name)
-                    }
+                    relation_data = {}
+
+                    if field_name in resource:
+                        relation_data.update({
+                            'data': resource.get(field_name),
+                            'meta': {
+                                'count': len(resource.get(field_name))
+                            }
+                        })
 
                     field_links = field.child_relation.get_links(
                         resource_instance,
@@ -200,13 +208,7 @@ def extract_relationships(cls, fields, resource, resource_instance):
                         {'links': field_links}
                         if field_links else dict()
                     )
-                    relation_data.update(
-                        {
-                            'meta': {
-                                'count': len(resource.get(field_name))
-                            }
-                        }
-                    )
+
                     data.update({field_name: relation_data})
                     continue