3.2.7. Mapping secondary tables
You can map a single entity bean to several tables using the
@SecondaryTable or @SecondaryTables class level annotations. To express that a column is in a particular table, use the table parameter of @Column or @JoinColumn.
@Entity
@Table(name="MainCat")
@SecondaryTables({ @SecondaryTable(name="Cat1", pkJoinColumns={ @PrimaryKeyJoinColumn(name="cat_id", referencedColumnName="id") ), @SecondaryTable(name="Cat2", uniqueConstraints={@UniqueConstraint(columnNames={"storyPart2"})}) })
public class Cat implements Serializable {
private Integer id;
private String name;
private String storyPart1;
private String storyPart2;
@Id @GeneratedValue
public Integer getId() {
return id;
}
public String getName() {
return name;
}
@Column(table="Cat1")
public String getStoryPart1() {
return storyPart1;
}
@Column(table="Cat2")
public String getStoryPart2() {
return storyPart2;
}
In this example,
name will be in MainCat. storyPart1 will be in Cat1 and storyPart2 will be in Cat2. Cat1 will be joined to MainCat using the cat_id as a foreign key, and Cat2 using id (ie the same column name, the MainCat id column has). Plus a unique constraint on storyPart2 has been set.
Check out the JBoss EJB 3 tutorial or the Hibernate Annotations unit test suite for more examples.