adding capability to extract json (to_json) using the field names and instead of the defined db_names, if those are set

tests/document/json_serialisation.py

@@ -20,6 +20,28 @@ class TestJson(unittest.TestCase):
     def setUp(self):
         connect(db='mongoenginetest')
 
+    def test_json_names(self):
+        """
+        Going to test reported issue:
+            https://github.com/MongoEngine/mongoengine/issues/654
+        where the reporter asks for the availability to perform
+        a to_json with the original class names and not the abreviated
+        mongodb document keys
+        """
+        class Embedded(EmbeddedDocument):
+            string = StringField(db_field='s')
+
+        class Doc(Document):
+            string = StringField(db_field='s')
+            embedded = EmbeddedDocumentField(Embedded, db_field='e')
+
+        doc = Doc( string="Hello", embedded=Embedded(string="Inner Hello"))
+        doc_json = doc.to_json(sort_keys=True, use_db_field=False,separators=(',', ':'))
+
+        expected_json = """{"embedded":{"string":"Inner Hello"},"string":"Hello"}"""
+
+        self.assertEqual( doc_json, expected_json)
+
     def test_json_simple(self):
 
         class Embedded(EmbeddedDocument):