#4917 - Remove O(n) queries in m2m updates

rest_framework/relations.py

@@ -491,11 +491,14 @@ class ManyRelatedField(Field):
             self.fail('not_a_list', input_type=type(data).__name__)
         if not self.allow_empty and len(data) == 0:
             self.fail('empty')
+            
+        values = list(self.child_relation.get_queryset.filter(pk__in=data))
+        missing_primary_keys = set(v.pk for v in values) - set(data)
+        
+        if missing_primary_keys:
+            self.fail('missing_ids', ids_not_found=list(missing_primary_keys))
 
-        return [
-            self.child_relation.to_internal_value(item)
-            for item in data
-        ]
+        return values
 
     def get_attribute(self, instance):
         # Can't have any relationships if not created