Help with Composite key

spiralhead · **Joined:** Tue Apr 17, 2007 7:57 pm **Posts:** 6

I can't figure this out.

I have a table, UserSites, which has a many-to-one relationship to Users.

i need the columns, "id" and "site_label" to be the composite primary key where "id" is a foreign key to Users.id and "site_label" is a user-defined site name that needs to be unique for a given user.

How do I set this up using annotations? Thanks in advance!

cpatni · **Joined:** Sun Apr 22, 2007 12:57 am **Posts:** 7

There are two ways of doing it.

1. Use @IdClass

Code:

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.OneToMany;
import javax.persistence.ManyToOne;
import java.io.Serializable;
import java.util.Collection;
@Entity
public class User {
  public int id;

  @OneToMany(mappedBy = "user")
  public Collection<UserSite> sites;

  public static class UserSitePk implements Serializable {
    @ManyToOne
    public User user;

    public String name;
  }
  
  @Entity
  @IdClass(UserSitePk.class)
  public static class UserSite {
    @Id
    public User user;

    @Id
    public String name;
  }
}

2. Use @EmbeddedId and @Embeddable

Code:

import javax.persistence.Embeddable;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import java.io.Serializable;
import java.util.Collection;
@Entity
public class User {
  public int id;

  @OneToMany(mappedBy = "id.user")
  public Collection<UserSite> sites;

  @Embeddable
  public static class UserSitePk implements Serializable {
    @ManyToOne
    public User user;
    public String name;
  }

  @Entity
  public static class UserSite {
    @EmbeddedId
    public UserSitePk id;

  }
}

spiralhead · **Joined:** Tue Apr 17, 2007 7:57 pm **Posts:** 6

Thank you so much sir. This is exactly what I needed.

Somebody should copy-paste this into the documentation :P

emmanuel · **Posted:** Mon Apr 23, 2007 6:17 am

If it's not in the doc, and if you provide a patch, I will apply it.

spiralhead · **Joined:** Tue Apr 17, 2007 7:57 pm **Posts:** 6

I think it's in the docs--just not explained so concisely as this.