private Object retrieveInstance(ExtObjectContainer client) {
   Query query = client.query();
   query.constrain(_class);
   query.descend("_isRoot").constrain(new Boolean(true));
   return query.execute().next();
 }
 private void assertNoItemFoundByQuery() {
   Query q = db().query();
   q.constrain(Item.class);
   Assert.areEqual(0, q.execute().size());
 }
 private void asserItemCount(final int expectedCount) {
   Query query = db().query();
   query.constrain(Item.class);
   int itemCount = query.execute().size();
   Assert.areEqual(expectedCount, itemCount);
 }