respect db fields in multiple layers of embedded docs

mongoengine/base/document.py

@@ -684,8 +684,13 @@ class BaseDocument(object):
         # class if unavailable
         class_name = son.get('_cls', cls._class_name)
 
-        # Convert SON to a dict, making sure each key is a string
-        data = {str(key): value for key, value in son.iteritems()}
+        # Convert SON to a data dict, making sure each key is a string and
+        # corresponds to the right db field.
+        data = {}
+        for key, value in son.iteritems():
+            key = str(key)
+            key = cls._db_field_map.get(key, key)
+            data[key] = value
 
         # Return correct subclass for document type
         if class_name != cls._class_name:

tests/fields/fields.py

@@ -1883,6 +1883,29 @@ class FieldTest(MongoDBTestCase):
         doc = self.db.test.find_one()
         self.assertEqual(doc['x']['i'], 2)
 
+    def test_double_embedded_db_field(self):
+        """Make sure that multiple layers of embedded fields resolve db
+        fields properly and can be initialized using dicts.
+        """
+        class C(EmbeddedDocument):
+            txt = StringField()
+
+        class B(EmbeddedDocument):
+            c = EmbeddedDocumentField(C, db_field='fc')
+
+        class A(Document):
+            b = EmbeddedDocumentField(B, db_field='fb')
+
+        a = A(
+            b=B(
+                c=C(txt='hi')
+            )
+        )
+        a.validate()
+
+        a = A(b={'c': {'txt': 'hi'}})
+        a.validate()
+
     def test_embedded_document_validation(self):
         """Ensure that invalid embedded documents cannot be assigned to
         embedded document fields.