filtering queryset before bulk update to guarantee all objects in json are found in db

rest_framework_bulk/drf3/serializers.py

@@ -1,4 +1,5 @@
 from __future__ import print_function, unicode_literals
+from rest_framework.exceptions import ValidationError
 from rest_framework.serializers import ListSerializer
 
 
@@ -32,7 +33,7 @@ class BulkSerializerMixin(object):
 class BulkListSerializer(ListSerializer):
     update_lookup_field = 'id'
 
-    def update(self, instances, all_validated_data):
+    def update(self, queryset, all_validated_data):
         id_attr = getattr(self.child.Meta, 'update_lookup_field', 'id')
 
         all_validated_data_by_id = {
@@ -40,9 +41,19 @@ class BulkListSerializer(ListSerializer):
             for i in all_validated_data
         }
 
+        # since this method is given a queryset which can have many
+        # model instances, first find all objects to update
+        # and only then update the models
+        objects_to_update = queryset.filter(**{
+            '{}__in'.format(id_attr): all_validated_data_by_id.keys(),
+        })
+
+        if len(all_validated_data_by_id) != objects_to_update.count():
+            raise ValidationError('Could not find find all objects to update.')
+
         updated_objects = []
 
-        for obj in instances:
+        for obj in objects_to_update:
             obj_id = getattr(obj, id_attr, None)
             obj_validated_data = all_validated_data_by_id.get(obj_id)
             if obj_id and obj_validated_data: