Re: [hibernate-dev] Pull request for HHH-2394 (Support filter tag in subclass)

> It seemed that the challenge to overcome was that Hibernate did not > know which aliases to use when generating the where clauses for > filters. When filters are not allowed on subclasses (current > situation), the alias for the root entity is used for all where > clauses. So when FilterHelper is asked to render the filters, it does > so with a single alias string. > So my changes revolve around two themes: > > 1. Remembering the filter's associated table so that we can generate > an appropriate alias. This was done by replacing the name->condition > map with a list of FilterConfiguration objects. This is a new class > and includes a qualified table name (as well as the name and > condition, of course). > > 2. Passing a callback (instead of the alias string) to > FilterHelper.render() that allows it to generate an appropriate alias > for each filter, depending on table name. The callback is an > implementation of a new interface, FilterAliasGenerator. The > implementation varies by context. The same problem exists in Criteria queries (HHH-1161) when using the sqlRestriction. In that use case, one uses the string '{alias}' as a placeholder in the SQL, and the engine replaces it, however as with your problem, it always replaces with the subclass alias, and therefore cannot be used to create a restriction on any superclass properties. It seems a more generic approach to the '{alias}' syntax which allows for, perhaps, '{entityName.alias}' (e.g. '{com.example.Mammal.alias}.is_pregnant = 1' would work, then your filter conditions wouldn't need the "table" attribute, and the fix would possibly be extensible for HHH-1161.

Alternatively, there are already some annotations which take an entity directly (such as @ManyToOne), as a class reference, which is way more typesafe and refactoring friendly. So instead of "table='ZOOLOGY_MAMMAL'" you could have "entity=Mammal.class". This would require more bookeeping on the implementation side, but would be a superior abstraction IMHO.