entity-bean-transactions

Both BMP and CMP entity beans have lifecycle callbacks (ejbLoad, ejbStore) that are called by the container, not the bean itself. If a developer tries to use programmatic transactions (begin/commit in code), they can’t control when ejbLoad/ejbStore are called — leading to uncommitted transactions and data inconsistency.

Entity Beans (BMP and CMP) MUST use Container-Managed (Declarative) Transactions only. Programmatic (Bean-Managed) Transactions are ILLEGAL for entity beans. This is the “Golden Rule” of EJB transactions.

1. When a transaction calls an entity bean, container calls ejbLoad() first (loads DB data, acquires locks)
2. Business methods execute within the transaction
3. On commit, container calls ejbStore() (writes to DB, releases locks)
4. Transaction spans: ejbLoad() → business methods → ejbStore()
5. If entity beans used BMT: developer would call begin() in ejbLoad(), but container controls when ejbLoad() is called — so the transaction may never properly complete
6. Entity beans load/store data per transaction, not per method call — the container optimizes when to actually hit the database

• Mandatory CMT: Entity beans (BMP and CMP) MUST use container-managed transactions
• BMT is illegal: Programmatic transactions cannot be used with entity beans
• Transaction spans ejbLoad → business methods → ejbStore (not per-method)
• Entity beans load/store per transaction, not per method call (performance implication)
• Session beans and MDBs CAN use BMT or CMT (entity beans cannot)

• Built from: Transaction Demarcation — entity beans restricted to CMT only
• Built from: Entity Bean — rule applies to all entity beans (BMP and CMP)
• Built from: ejbLoad() — called by container within transaction
• Built from: ejbStore() — called by container within transaction
• Contrasts with: Session Bean — session beans can use BMT or CMT
• Contrasts with: MDB — MDBs can use BMT or CMT
• Related: CMT vs BMT — why CMT is mandatory for entities

• Performance problem: if each method call is a separate transaction, entity bean does DB read/write per get/set
• Solution: make transactions span multiple method calls (using transaction attributes)
• BMP developers often mistakenly try BMT — it’s explicitly illegal in EJB spec
• Entity beans don’t control when ejbLoad/ejbStore are called — container does