How to get a unique key for two fields with Hibernate?

Question

I have two fields of an entity class which I don\'t want to be unique but to instead be used as composite fields for a key which must itself be unique. For example I have t

Answer 1

We usually will wrap the two fields in an inner key class which is marked as @Embeddable. For example:

@Entity
public class Foo {

  @EmbeddedId()
  private Key key;
  ...

  @Embeddable
  public static class Key {
    @Column(nullable=false)
    private String name;
    @Column(nullable=false)
    private int version;

    protected Key () {
      // for hibernate
    }
    public Key (String name, int version) {
      this.name = name;
      this.version = version;
    }
    ...
    // You probably want .equals and .hashcode methods
  }
}

Answer 2

This will create a unique key on the database:

@Table( name = "MYTABLE",
        uniqueConstraints = { @UniqueConstraint( columnNames = { "NAME", "VERSION" } ) } )

This will be enforced by the database on a update or persist.

You'd need to write your own custom validator if you wanted to enforce this using Hibernate Validator.