Sorry some debugging of mine.

Actually I think I'll need to rethink this PR. I think I can actually reuse the various count, slice, exists... method of the persistentCollection. The problem is that because of the additional criteria, I should make those various methods aware of the Criteria...

For now I'll let this as a WIP and try to come up for a solution if I have some time. But really, I think all those part should be rewritten from scratch...