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

[Rob Worsnop]

https://github.com/hibernate/hibernate-orm/pull/339

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.


Where filters are applied to entities, we know the table name. When
filters are applied to collections we do not. My solution to this is
potentially controversial and I'd be interested in hearing
alternatives to it. I have expanded the @Filter annotation to include
a table name. This is an optional element because it makes no sense
when @Filter is applied directly to an entity. That's what I don't
like about this idea.

For example:

	@OneToMany(mappedBy="club")
	@Filters({
		@Filter(name="iqMin", table="ZOOLOGY_HUMAN", condition="HUMAN_IQ >= :min"),
		@Filter(name="pregnantMembers", table="ZOOLOGY_MAMMAL",
condition="IS_PREGNANT=1")
	})
	private Set<Human> members = new HashSet<Human>();

This is excerpted from here:
https://github.com/rworsnop/hibernate-orm/blob/HHH-2394/hibernate-core/src/matrix/java/org/hibernate/test/annotations/filter/subclass/joined/Club.java

Thoughts?