Sun Microsystem Inc

9.4.5 ejbStore

When the container needs to synchronize the state of the entity object in the database with the state of the enterprise bean instance, the container first calls the ejbStore() method on the instance, and then it extracts the container-managed fields and writes them to the database.

The entity Bean Provider should use the ejbStore() method to set up the values of the con- tainer-managed fields just before the container writes them to the database. For example, the ejbStore() method may perform compression of text before the text is stored in the database.

9.4.6 finder methods

The entity Bean Provider does not write the finder ( ejbFind<METHOD>(...)) methods.

The finder methods are generated at the entity bean deployment time using the container provider’s tools. The tools can, for example, create a subclass of the entity bean class that implements the ejbFind<METHOD>() methods, or the tools can generate the implementation of the finder methods directly in the class that implements the entity bean’s home interface.

Note that the ejbFind<METHOD> names and parameter signatures do not provide the container tools with sufficient information for automatically generating the implementation of the finder methods for methods other than ejbFindByPrimaryKey. Therefore, the bean provider is responsible for providing a description of each finder method. The entity bean Deployer uses container tools to generate the implementation of the finder methods based in the description supplied by the bean provider. The Enterprise JavaBeans architecture does not specify the format of the finder method description.

9.4.7 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 9.2.9.

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.

Sun Microsystems Inc.

9.4.7.1 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.

9.4.7.2 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.)

9.4.7.3 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).

In this special case, the type of the argument of the findByPrimaryKey method must be declared as java.lang.Object, and the return value of ejbCreate() must be declared as java.lang.Object. The Bean Provider must specify the primary key class in the deployment descriptor as of the type java.lang.Object.

The primary key class is specified at deployment time in the situations when the Bean Provider develops an entity bean that is intended to be used with multiple back-ends that provide persistence, and when these multiple back-ends require different primary key structures.

Use of entity beans with a deferred primary key type specification limits the client application programming model, because the clients written prior to deployment of the entity bean may not use, in general, the methods that rely on the knowledge of the primary key type.

The implementation of the enterprise bean class methods must be done carefully. For example, the methods should not depend on the type of the object returned from EntityContext.getPrimaryKey(), because the return type is determined by the Deployer after the EJB class has been written.