jpa Relations between entities @JoinTable Annotation Example

Example

When mapping many-to-many relationships in JPA, configuration for the table used for the joining foreign-keys can be provided using the @JoinTable annotation:

@Entity
public class EntityA {
   @Id
   @Column(name="id")
   private long id;
   [...]
   @ManyToMany
   @JoinTable(name="table_join_A_B",
              joinColumns=@JoinColumn(name="id_A"), referencedColumnName="id"
              inverseJoinColumns=@JoinColumn(name="id_B", referencedColumnName="id"))
   private List<EntityB> entitiesB;
   [...]
}

@Entity
public class EntityB {
   @Id
   @Column(name="id")
   private long id;
   [...]
}

In this example, which consists of EntityA having a many-to-many relation to EntityB, realized by the entitiesB field, we use the @JoinTable annotation to specify that the table name for the join table is table_join_A_B, composed by the columns id_A and id_B, foreign keys respectively referencing column id in EntityA's table and in EntityB's table; (id_A,id_B) will be a composite primary-key for table_join_A_B table.