[jboss-user] [JBoss Seam] - Re: Seam application with tree on left and editor for select

christian.bauer@jboss.com do-not-reply at jboss.com
Thu Oct 26 10:49:15 EDT 2006

You have to understand how a/the persistence context works. The persistence context is a cache, basically an identity map that has as keys the primary keys of database rows, and as values some Java instances. During one conversation, no matter how it it gets there (find by identifier, query, lazy initialization), I have one persistence context and one identity map. 

You can manage a persistence context. The EntityManager API has clear() and the Hibernate Session API also evict(o) for single instances.

You can load stuff into the persistence context any way you want, the important thing is to keep the identity scope so that at most you have one in-memory representation of a particular database row. Without this, you would work with detached objects, a totally different concept that implies much more manual work.

Read this: http://www.manning.com/bauer2

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