How to resolve many-to-many relationship without creating a junction class in Java?

Question

In my DB I have three table USER, PERMISSION and a junction table USER_PERMISSIONS. As you can see I have clear many-to-many relationship.

And here is the question. I'm using a Hibernate. Is it possible to use only two classes, User and Permissions without creating a junction class UserPermissions? I mean can I use some kind of annotations to include my junction table USER_PERMISSIONS?

Answer 1

Yes you can. You need to use the @JoinTable and @JoinColumn annotation. Example below:

@Entity
@Table(name = "USER")
public class User {

@Id
@Column(name = "ID")
private Long id;

@ManyToMany
@JoinTable(name = "USER_PERMISSIONS", 
    joinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "ID"), 
    inverseJoinColumns = @JoinColumn(name = "PERM_ID", referencedColumnName = "ID"))
private Collection<Permissions> permissions;

A full working example with bidirectionaly many to many can be found in here http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany