Putting unique constraint on multiple fields

Question

Let's say I have an entity like this:

@Entity
public Foo {
    @Id
    private Long id;

    private String name;

    private String type;

    ...
}

Is there a way to express that name and type should be unique together? Meaning that for example you could have name "x" with type "y" and name "x" with type "z", but not an other "x" with type "y".

@EmbeddedId doesn't do the trick since name can be changed later - type however remains the same throughout the lifecycle of the entity.

You need to look into constraints. [This should answer your question](http://stackoverflow.com/questions/2772470/how-to-introduce-multi-column-constraint-with-jpa-annotations). — Sotirios Delimanolis, May 06 '13 at 15:13
ok,that's the answer - sadly I cannot accept a comment, so make it an answer, and I'll accept it. Thanks! — Zoltán, May 06 '13 at 15:17
I added an answer below with a reference you might want to look at for more info. — Sotirios Delimanolis, May 06 '13 at 15:21

score 2 · Accepted Answer · answered May 06 '13 at 15:19

You can add Constraints for your Entity on the @Table annotation. In your case, you want to make two joined fields unique. You would use the @UniqueConstraint annotation.

@Entity
@Table(uniqueConstraints=
           @UniqueConstraint(columnNames = {"name", "type"}) 
public Foo {
    @Id
    private Long id;
    @Column
    private String name;
    @Column    
    private String type;

    ...
}

Take a look at the javadoc for @UniqueConstraint.

Putting unique constraint on multiple fields

1 Answers1