Enterprise JavaBeans, Second Edition

Entity Bean Relationships

Business systems frequently define relationships between entity beans. These relationships can be complex or simple. The concept of a cabin and its relationship to a ship embodies both simple and complex relationships. A cabin always belongs to a particular ship—a relationship that’s obviously fairly simple. From the ship’s perspective, the relationship is more complex: a ship has many cabins and must maintain a relationship to all of them.

This section explores how to write entity beans that use container-managed persistence and maintain relationships with other beans. This information will be most useful to EJB 1.0 developers. EJB 1.0 does not allow references to other beans to be container-managed. This means that a bean needs to manage persistence for references to other beans within its own code.

If you’re using EJB 1.1, you can probably ignore this section, particularly if your server has robust support for the persistence of bean references. While EJB 1.1 allows bean references to be container-managed fields, a few EJB 1.1 servers may not be able to persist relationships between beans. This section will be useful to developers using these limited EJB 1.1 servers. EJB 1.1 developers using bean-managed persistence may also find the strategies in this section useful.

However, since this is predominately a EJB 1.0 problem, the code in this section has been left in the EJB 1.0 style. EJB 1.1 developers must make minor changes to the code for it to work ...