Filter by subclass attributes

This add support for filtering by subclass properties. It allows to filter associated properties (last persistent property can be in subclass) as well as direct persistent properties of subclasses.

It is not possible to filter by association which starts in some subclass. It is also not possible to filter by subclass attribute if the db schema uses table-per-hierarchy structure. These is not supported by criteria itself.

Documentation is missing I would suggest separate chapter for sub class properties filtering. Should I write it?