JDO + GoogleAppEngine - search class by value in collection

Question

Hi,

I'm making application running on Google App Engine and I'm having problem with getting data using JDO. I have class Message, which has property private List<String> labels;. Now I want to have some search function which takes one string (label) as a parameter and searches all messages to get messages with given label. The problem is with the JDO query, right now I have this (string this.label is a search parameter):

   String query = "select from " + Message.class.getName() + " where (labels.contains('" + this.label + "')) ";

It works on localhost, but not in GAE (returns NULL). Another (and naive) attempt was

   query = "select from " + Note.class.getName() + " where labels=='" + this.label + "'";

And it also worked only on localhost, not GAE

Does anybody have an idea how to do that? Thanks for any help