Multi-Column Join in Hibernate/JPA Annotations
- by bowsie
I have two entities which I would like to join through multiple columns. These columns are shared by an @Embeddable object that is shared by both entities. In the example below, Foo can have only one Bar but Bar can have multiple Foos (where AnEmbeddableObject is a unique key for Bar). Here is an example:
@Entity
@Table(name = "foo")
public class Foo {
@Id
@Column(name = "id")
@GeneratedValue(generator = "seqGen")
@SequenceGenerator(name = "seqGen", sequenceName = "FOO_ID_SEQ", allocationSize = 1)
private Long id;
@Embedded
private AnEmbeddableObject anEmbeddableObject;
@ManyToOne(targetEntity = Bar.class, fetch = FetchType.LAZY)
@JoinColumns( {
@JoinColumn(name = "column_1", referencedColumnName = "column_1"),
@JoinColumn(name = "column_2", referencedColumnName = "column_2"),
@JoinColumn(name = "column_3", referencedColumnName = "column_3"),
@JoinColumn(name = "column_4", referencedColumnName = "column_4")
})
private Bar bar;
// ... rest of class
}
And the Bar class:
@Entity
@Table(name = "bar")
public class Bar {
@Id
@Column(name = "id")
@GeneratedValue(generator = "seqGen")
@SequenceGenerator(name = "seqGen", sequenceName = "BAR_ID_SEQ", allocationSize = 1)
private Long id;
@Embedded
private AnEmbeddableObject anEmbeddableObject;
// ... rest of class
}
Finally the AnEmbeddedObject class:
@Embeddable
public class AnEmbeddedObject {
@Column(name = "column_1")
private Long column1;
@Column(name = "column_2")
private Long column2;
@Column(name = "column_3")
private Long column3;
@Column(name = "column_4")
private Long column4;
// ... rest of class
}
Obviously the schema is poorly normalised, it is a restriction that AnEmbeddedObject's fields are repeated in each table.
The problem I have is that I receive this error when I try to start up Hibernate:
org.hibernate.AnnotationException: referencedColumnNames(column_1, column_2, column_3, column_4) of Foo.bar referencing Bar not mapped to a single property
I have tried marking the JoinColumns are not insertable and updatable, but with no luck. Is there a way to express this with Hibernate/JPA annotations?
Thank you.
