JPA: directly mapping collection size to attribute using count?

Question

Class A has a one-to-many relationship to B. Hence, A has an attribute collectionOfB.

Is there any way I could map "count B" to single attribute in A?

The purpose would be to offer a shortcut to retrieve the number of associated Bs without loading the entire collection. Sometimes all I need is the count i.e. the collection size. I know I could issue a query against the entity manager that does exactly that. However, seeing it done by the JPA provider thanks to annotations would of course be preferable.

Answer 1

I was able to solve my problem using Hibernate's extra-lazy mapping: http://www.frightanic.com/2010/11/21/extra-lazy-one-to-many-mapping-with-hibernate/