From 4af78d601623ef6b2f0609340797480fa2c85032 Mon Sep 17 00:00:00 2001
From: Manuel Schraner <manuel.schraner@gmail.com>
Date: Tue, 8 Mar 2016 06:00:40 +0100
Subject: [PATCH 1/2] fix for issue #904, also includes a test which checks the
 error case I reported in the issue report.

---
 mongoengine/base/document.py |  7 ++++++-
 tests/document/db_fields.py  | 37 ++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 tests/document/db_fields.py

diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index 3eba16ca8..d683e54cb 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -686,7 +686,12 @@ def _from_son(cls, son, _auto_dereference=True, only_fields=None, created=False)
         # get the class name from the document, falling back to the given
         # class if unavailable
         class_name = son.get('_cls', cls._class_name)
-        data = dict(("%s" % key, value) for key, value in son.iteritems())
+        if PY3:
+            son_gen = son.items()
+        else:
+            son_gen = son.iteritems()
+
+        data = dict(("%s" % cls._db_field_map.get(key,key), value) for key, value in son_gen)
 
         # Return correct subclass for document type
         if class_name != cls._class_name:
diff --git a/tests/document/db_fields.py b/tests/document/db_fields.py
new file mode 100644
index 000000000..d2a0abdea
--- /dev/null
+++ b/tests/document/db_fields.py
@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+import sys
+sys.path[0:0] = [""]
+import unittest
+from mongoengine import *
+
+__all__ = ("DbFieldParameterTest", )
+
+
+class DbFieldParameterTest(unittest.TestCase):
+
+    def test_document_db_field_validation(self):
+
+        # https://github.com/MongoEngine/mongoengine/issues/904
+
+        data = {'b': {'c': [{'x': 1.0, 'y': 2.0}]}}
+
+        class C(EmbeddedDocument):
+            x = FloatField(db_field='fx')
+            y = FloatField(db_field='fy')
+
+        class B(EmbeddedDocument):
+            c = ListField(EmbeddedDocumentField(C), db_field='fc')
+
+        class A(Document):
+            b = EmbeddedDocumentField(B, db_field='fb')
+
+        a = A(**data)
+
+        try:
+            a.validate()
+        except ValidationError as e:
+            self.fail("ValidationError raised: %s" % e.message)
+
+
+if __name__ == '__main__':
+    unittest.main()

From dc03a6c0964678f65fef77e298004971f907fd09 Mon Sep 17 00:00:00 2001
From: Manuel Schraner <manuel.schraner@gmail.com>
Date: Tue, 8 Mar 2016 12:35:17 +0100
Subject: [PATCH 2/2] python 3 code is handled by 2to3; test for db_field
 translation to and from SON.

---
 mongoengine/base/document.py |  7 +------
 tests/document/db_fields.py  | 24 ++++++++++++++++++------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index d683e54cb..8faa1f523 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -686,12 +686,7 @@ def _from_son(cls, son, _auto_dereference=True, only_fields=None, created=False)
         # get the class name from the document, falling back to the given
         # class if unavailable
         class_name = son.get('_cls', cls._class_name)
-        if PY3:
-            son_gen = son.items()
-        else:
-            son_gen = son.iteritems()
-
-        data = dict(("%s" % cls._db_field_map.get(key,key), value) for key, value in son_gen)
+        data = dict(("%s" % cls._db_field_map.get(key,key), value) for key, value in son.iteritems())
 
         # Return correct subclass for document type
         if class_name != cls._class_name:
diff --git a/tests/document/db_fields.py b/tests/document/db_fields.py
index d2a0abdea..ada0386d0 100644
--- a/tests/document/db_fields.py
+++ b/tests/document/db_fields.py
@@ -2,6 +2,8 @@
 import sys
 sys.path[0:0] = [""]
 import unittest
+
+from bson import SON
 from mongoengine import *
 
 __all__ = ("DbFieldParameterTest", )
@@ -9,11 +11,10 @@
 
 class DbFieldParameterTest(unittest.TestCase):
 
-    def test_document_db_field_validation(self):
-
-        # https://github.com/MongoEngine/mongoengine/issues/904
-
-        data = {'b': {'c': [{'x': 1.0, 'y': 2.0}]}}
+    def setUp(self):
+        # testcase from https://github.com/MongoEngine/mongoengine/issues/904
+        self.data = {'b': {'c': [{'x': 1.0, 'y': 2.0}]}}
+        self.reference_son = SON([('fb', SON([('fc', [SON([('fx', 1.0), ('fy', 2.0)])])]))])
 
         class C(EmbeddedDocument):
             x = FloatField(db_field='fx')
@@ -25,13 +26,24 @@ class B(EmbeddedDocument):
         class A(Document):
             b = EmbeddedDocumentField(B, db_field='fb')
 
-        a = A(**data)
+        self.A = A
 
+    def test_document_db_field_validation(self):
+        a = self.A(**self.data)
         try:
             a.validate()
         except ValidationError as e:
             self.fail("ValidationError raised: %s" % e.message)
 
+    def test_document_fieldname_to_db_field_name(self):
+        a = self.A(**self.data)
+        self.assertEqual(a.to_mongo(), self.reference_son)
+
+    def test_document_db_fieldname_to_fieldname(self):
+        a = self.A._from_son(self.reference_son)
+        self.assertEqual(a.b.c[0].x, 1.0)
+        self.assertEqual(a.b.c[0].y, 2.0)
+
 
 if __name__ == '__main__':
     unittest.main()