Enterprise JavaBeans 3.1, 6th Edition

Nonentity Base Classes

The inheritance mappings we described so far in this chapter concerned a class hierarchy of entity beans. Sometimes, however, you need to inherit from a nonentity superclass. This superclass may be an existing class in your domain model that you do not want to make an entity. The @javax.persistence.MappedSuperclass annotation allows you to define this kind of mapping. Let’s modify our example class hierarchy and change Person into a mapped superclass:

@MappedSuperclass
public class Person
{
   @Id @GeneratedValue
   public int getId( ) { return id; }
   public void setId(int id) { this.id = is; }
   ...
}

@Entity
@Table(name="CUSTOMER")
@Inheritance(strategy=InheritanceType.JOINED)
@AttributeOverride(name="lastname", column=@Column(name="SURNAME"))
public class Customer extends Person {
...
}

@Entity
@Table(name="EMPLOYEE")
@PrimaryKeyJoinColumn(name="EMP_PK")
public class Employee extends Customer {
...
}

Since it is not an entity, the mapped superclass does not have an associated table. Any subclass inherits the persistence properties of the base class. You can override any mapped property of the mapped class by using the @javax.persistence.AttributeOverride annotation.

You can have @MappedSuperclass annotated classes in between two @Entity annotated classes in a given hierarchy. Also, nonannotated classes (i.e., not annotated with @Entity or @MappedSuperclass) are completely ignored by the persistence provider.