What Kind of Generation to Use?

You may face two situations when generating EJB source code:

You have no database
You already have a database

You want to generate EJB source code when creating a database. If there is no database, the development process is the following:

Define persistent objects in the class diagram, and define EJBs in the component diagram
Generate the Physical Data Model, with creation of an O/R Mapping during generation
Create the database
Generate EJB source code and deployment descriptor for deployment in the application server

You want to generate EJB source code for an existing database. If the database already exists, you may want to wrap the existing database into EJBs and use EJBs to access the database.The development process is the following:

Reverse engineer the PDM into an OOM, and retrieve the O/R mapping generated during reverse
Define EJBs in the OOM based on persistent classes
Generate the EJB source code and deployment descriptor for deployment in the application server

You can also use generation of EJB source code when managing persistence of EJBs with an existing database. For example, it may be necessary to manage the persistence of an already defined EJB with an existing database. Since you cannot change the definition of EJB nor the database schema, you need a manual object to relational mapping in this case.

For more information on object mapping, see Object/Relational (O/R) Mapping.