Enterprise JavaBeans, Fourth Edition

The Query Methods

There are two main types of query methods: find methods and select methods. These are discussed in the following sections.

Find Methods

Find methods are invoked by EJB clients (applications or beans) to obtain EJB object references to specific entity beans. For example, you might call the findByPrimaryKey( ) method on the Customer EJB’s home interface to obtain a reference to a specific Customer bean.

Find methods are always declared in the local and remote home interfaces of an entity bean. Specifying a single remote or local return type for a find method indicates that the method locates only one bean. findByPrimaryKey( ) obviously returns a single remote reference, because there is a one-to-one correspondence between a primary key’s value and an entity. Other single-entity find methods can also be declared. For example, in the following code segment the Customer EJB declares several single-entity find methods, each of which supports a different query:

public interface CustomerHomeRemote extends javax.ejb.EJBHome {
    public CustomerRemote findByPrimaryKey(Integer primaryKey)
        throws javax.ejb.FinderException, java.rmi.RemoteException;

    public CustomerRemote findByName(String lastName, String firstName)
        throws javax.ejb.FinderException, java.rmi.RemoteException;

    public CustomerRemote findBySSN(String socialSecurityNumber)
        throws javax.ejb.FinderException, java.rmi.RemoteException;
}

Bean developers can also define multi-entity find methods, which return a collection ...