Sun Microsystems Inc.

EJB 1.1 Entity Bean Component Contract for Container Managed PersistenceEnterprise JavaBeans 2.0, Public Draft EJB 1.1 Entity

13.1.9 primary key type

The container must be able to manipulate the primary key type. Therefore, the primary key type for an entity bean with container-managed persistence must follow the rules in this subsection, in addition to those specified in Subsection 11.2.10.

There are two ways to specify a primary key class for an entity bean with container-managed persistence:

•Primary key that maps to a single field in the entity bean class.

•Primary key that maps to multiple fields in the entity bean class.

The second method is necessary for implementing compound keys, and the first method is convenient for single-field keys. Without the first method, simple types such as String would have to be wrapped in a user-defined class.

13.1.9.1 Primary key that maps to a single field in the entity bean class

The Bean Provider uses the primkey-field element of the deployment descriptor to specify the container-managed field of the entity bean class that contains the primary key. The field’s type must be the primary key type.

13.1.9.2 Primary key that maps to multiple fields in the entity bean class

The primary key class must be public, and must have a public constructor with no parameters.

All fields in the primary key class must be declared as public.

The names of the fields in the primary key class must be a subset of the names of the container-managed fields. (This allows the container to extract the primary key fields from an instance’s container-managed fields, and vice versa.)

13.1.9.3 Special case: Unknown primary key class

In special situations, the entity Bean Provider may choose not to specify the primary key class for an entity bean with container-managed persistence. This case usually happens when the entity bean does not have a natural primary key, and the Bean Provider wants to allow the Deployer to select the primary key fields at deployment time. The entity bean’s primary key type will usually be derived from the primary key type used by the underlying database system that stores the entity objects. The primary key used by the database system may not be known to the Bean Provider.

When defining the primary key for the enterprise bean, the Deployer may sometimes need to subclass the entity bean class to add additional container-managed fields (this typically happens for entity beans that do not have a natural primary key, and the primary keys are system-generated by the underlying database system that stores the entity objects).