Container-managed persistence and relationships allow you to build components to the EJB 2.0 specification that can save the state of your EJBs to any J2EE supporting application server and database without having to create your own low-level JDBC-based persistence system. It also provides a unified way to support persistent fields and variables within entity beans. This two-part introductory tutorial explains all about CMP/CMR. EJB QL provides the ability to query the container-managed persistent store for EJB objects without the need to learn or make database specific calls. EJB QL provides a subset of SQL and adds support for traversing relationships between entities and working with collection-based CMP fields.
Introduction to container-managed persistence and relationships, Part 4 This tutorial completes Rick Hightower's series on container-managed persistence and relationships in EJB 2.x with a focus on EJB Query Language. This piece details advanced finder methods and more complex EJB-QL queries.