diff --git a/api/lib/database.py b/api/lib/database.py
index 7b50d38..cc43a56 100644
--- a/api/lib/database.py
+++ b/api/lib/database.py
@@ -10,9 +10,14 @@ from api.lib.exception import CommitException
 
 class FormatMixin(object):
     def to_dict(self):
-        return dict([(k.name, isinstance(getattr(self, k.name), datetime.datetime) and
-                      getattr(self, k.name).strftime('%Y-%m-%d %H:%M:%S')) or
-                     getattr(self, k.name) for k in getattr(self, "__table__").columns])
+        res = dict()
+        for k in getattr(self, "__table__").columns:
+            if not isinstance(getattr(self, k.name), datetime.datetime):
+                res[k.name] = getattr(self, k.name)
+            else:
+                res[k.name] = getattr(self, k.name).strftime('%Y-%m-%d %H:%M:%S')
+
+        return res
 
     @classmethod
     def get_columns(cls):