JPA persist many to many

I have a pretty standard scenario whereby I have a table of Users with user_id as the PK and a table of Roles with role_id as the PK. The two tables are related via a many to many relationship (ie. Users can have many roles and a role can be applied to many users) and subsequently I have a joining table called users_has_roles. The only two columns in users_has_roles are users_user_id and roles_role_id.

I have generated the entity classes (see below) and I have no problem persisting data to the users and roles tables but I have failed miserably persist anything to the users_has_roles joining table so currently none of my users are being assigned a role. Before I go crazy could somebody put me out of my misery and show me how I should go about adding a users_user_id with a corresponding roles_role_id to the users_has_roles table so my users can have roles?

My Users.java entity class:

@Entity
@Table(name = "users")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Users.findAll", query = "SELECT u FROM Users u"),
@NamedQuery(name = "Users.findByUserId", query = "SELECT u FROM Users u WHERE u.userId = :userId"),
@NamedQuery(name = "Users.findByUsername", query = "SELECT u FROM Users u WHERE u.username = :username"),
@NamedQuery(name = "Users.findByPassword", query = "SELECT u FROM Users u WHERE u.password = :password")})
public class Users implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 60)
@Column(name = "user_id")
private String userId;
@Basic(optional = false)
@NotNull
@Pattern(regexp="[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?", message="Invalid email")
@Size(min = 1, max = 45)
@Column(name = "username")
private String username;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 120)
@Column(name = "password")
private String password;
@JoinTa

Your example works fine (EclipseLink 2.3, MySQL). Likely problem is in part of the code that you do not show. For example in adding element to rolesCollection. Typical mistake is for example to add element only to the non owning side.

For persisting it you have to keep care about relation in owning side (one without mappedBy), for keeping also in-memory object graph consistent with database, you should always modify both sides of relation.

I tried it with following:

    // method to add element to rolesCollection
    public void addRoles(Roles r) {
        rolesCollection.add(r);
    }

    //first created new instances of Users and Roles
    // then:
    tx.begin();
    users.addRoles(r);
    //it is not needed for persisting, but here you can also
    //add user to roles.
    em.persist(users);
    em.persist(r);
    tx.commit();

answered 2012-04-22T09:10:04.433

JPA persist many to many

1 Answer

Your Answer