Allow atomic update for the entire DictField

AUTHORS

@@ -206,3 +206,4 @@ that much better:
  * Clay McClure (https://github.com/claymation)
  * Bruno Rocha (https://github.com/rochacbruno)
  * Norberto Leite (https://github.com/nleite)
+ * Bob Cribbs (https://github.com/bocribbz)

mongoengine/fields.py

@@ -826,6 +826,10 @@ class DictField(ComplexBaseField):
             return StringField().prepare_query_value(op, value)
 
         if hasattr(self.field, 'field'):
+            if op in ('set', 'unset') and isinstance(value, dict):
+                return dict(
+                    (k, self.field.prepare_query_value(op, v))
+                    for k, v in value.items())
             return self.field.prepare_query_value(op, value)
 
         return super(DictField, self).prepare_query_value(op, value)

tests/fields/fields.py

@@ -18,6 +18,7 @@ from bson import Binary, DBRef, ObjectId
 from mongoengine import *
 from mongoengine.connection import get_db
 from mongoengine.base import _document_registry
+from mongoengine.base.datastructures import BaseDict
 from mongoengine.errors import NotRegistered
 from mongoengine.python_support import PY3, b, bin_type
 
@@ -1251,6 +1252,30 @@ class FieldTest(unittest.TestCase):
 
         Simple.drop_collection()
 
+    def test_atomic_update_dict_field(self):
+        """Ensure that the entire DictField can be atomically updated."""
+
+
+        class Simple(Document):
+            mapping = DictField(field=ListField(IntField(required=True)))
+
+        Simple.drop_collection()
+
+        e = Simple()
+        e.mapping['someints'] = [1, 2]
+        e.save()
+        e.update(set__mapping={"ints": [3, 4]})
+        e.reload()
+        self.assertEqual(BaseDict, type(e.mapping))
+        self.assertEqual({"ints": [3, 4]}, e.mapping)
+
+        def create_invalid_mapping():
+            e.update(set__mapping={"somestrings": ["foo", "bar",]})
+
+        self.assertRaises(ValueError, create_invalid_mapping)
+
+        Simple.drop_collection()
+
     def test_mapfield(self):
         """Ensure that the MapField handles the declared type."""