Entity Beans

• Used to model persistent objects
• Object state is stored in a persistent data store, usually a relational or object database
• A primary key class is used to identify an individual object
• Lifecycle methods are used to locate objects and manage the persistence
  • Create new object (SQL Insert)
  • Destroy object (SQL Delete)
  • Save state (SQL Update)
  • Find an existing object and retrieve its state (SQL Select)
• Two ways to manage persistence
  • Container-managed persistence (CMP)
    • Tools are used to map object attributes to a database
    • The mapping is deployed to the EJB container
    • The container generates the necessary SQL at runtime
    • In EJB 1.1, CMP is limited to objects that map to a single database table (i.e. no dependent object, no table joins); this restriction is relaxed in EJB 2.0
  • Bean-managed persistence (BMP)
    • The application developer supplies the appropriate code in the various lifecycle methods
    • The EJB container calls the lifecycle methods when necessary