Head First EJB

Chapter 7. Entity Relationships: When Beans Relate

Entity beans need relationships. An Order needs a Customer. A LineItem needs an Order. An Order needs LineItems. A Movie needs a Director. A Director needs Movies. A Movie needs Actors. An Actor needs talent... Entity beans can have container-managed relationships (CMR) and the Container takes care of virtually everything. Make a new Movie and give it a Director? That Director automatically has one more Movie in his Movie collection. Make a new LineItem that’s related to an Order? If you ask the Customer to show you his Orders, his Orders will show the new LineItem. Best of all, you can use EJB-QL to write portable (think: vendor/databse independent) queries.

Objectives: Entity Relationships: CMP and CMR

Official:		What it really means:
6.2	Identify correct and incorrect statements or examples about persistent relationships, remove protocols, and about the abstract schema type, of a CMP entity bean.	You have to know that the container manages relationships between two entity beans through container-managed persistent (CMR) fields, and that CMR fields must be described in the deployment descriptor using the <relationships> section. You have to understand the implications of multiplicity in a relationship, and that the Container cares whether the relationship is one-to-one, one-to-many, or many-to-many. You must know that the Container maintains ...