Enterprise JavaBeans 3.1, 6th Edition

@Embedded Objects

The Java Persistence specification allows you to embed nonentity Java objects within your entity beans and map the properties of this embedded value object to columns within the entity’s table. These objects do not have any identity, and they are owned exclusively by their containing entity bean class. The rules are very similar to the @EmbeddedId primary-key example given earlier in this chapter. We first start out by defining our embedded object:

@Embeddable
public class Address implements java.io.Serializable
{
   private String street;
   private String city;
   private String state;

   public String getStreet() { return street; }
   public void setStreet(String street) { this.street = street; }
   public String getCity() { return city; }
   public void setCity(String city) { this.city = city; }
   public String getState() { return state; }
   public void setState(String state) { this.state = state; }
}

The embedded Address class has the @Column mappings defined directly within it. Next, let’s use the @javax.persistence.Embedded annotation within our Employee bean class to embed an instance of this Address class:

package javax.persistence;

public @interface Embedded {}

As with @EmbeddedId, the @Embedded annotation can be used in conjunction with the @AttributeOverrides annotation if you want to override the column mappings specified in the embedded class. The following example shows how this overriding is done. If you don’t want to override, leave out the @AttributeOverrides:

@Entity @Table(name="table_employees" ...