Fix long fields stored as int32 in Python 3. issue #1253

mongoengine/fields.py

@@ -19,7 +19,7 @@ else:
 
 import pymongo
 import gridfs
-from bson import Binary, DBRef, SON, ObjectId
+from bson import Binary, DBRef, SON, ObjectId, Int64
 
 from mongoengine.errors import ValidationError
 from mongoengine.python_support import (PY3, bin_type, txt_type,
@@ -227,6 +227,9 @@ class LongField(BaseField):
             pass
         return value
 
+    def to_mongo(self, value, **kwargs):
+        return Int64(value)
+
     def validate(self, value):
         try:
             value = long(value)