entity-bean-identity

Session beans are all equivalent (especially stateless)—there’s no way to distinguish one from another. But entity beans represent specific data records (like a specific bank account). How do you identify which entity bean instance represents which record?

Entity beans have an identity—a primary key that uniquely distinguishes each instance. This allows:

• Comparing two entity beans (“Are they the same account?”)
• Clients referring to specific entities by their primary key
• Sharing entities across multiple clients (unlike session beans which are client-dedicated)

The identity is typically the primary key of the database row the entity represents.

1. Define primary key class: AccountPK with fields matching the table’s primary key
2. getPrimaryKey() method: Entity beans implement this to return their primary key
3. Finder methods: ejbFindByPrimaryKey(PK) locates the correct database record
4. Client reference: Client can pass primary keys to other clients, enabling shared access

• Primary key = identity: Two entity beans with same PK represent the same data
• Shared across clients: Unlike session beans, multiple clients can use the same entity
• Not just for databases: Identity concept applies even if using object databases
• getPrimaryKey() in BMP: Bean uses PK to know which record to load/store in ejbLoad()/ejbStore()

• Built from: Entity Bean, Primary Key Class
• Builds into: Finder Methods (locate entities by identity)
• Related: ejbCreate(), ejbLoad(), ejbStore()
• Contrasts with: Session Bean (no identity—anonymous workers)

• Composite primary keys: Sometimes PK has multiple fields—need a custom PK class
• Identity crisis in pool: Pooled entity beans can represent different records at different times (container swaps the data)
• getPrimaryKey() not for clients: It’s for BMP beans to know which record to access