Database:
users (User Table)
id (primary key)
username
...
referral (Referral Table)
id (primary key)
name
...
Referral_User_Queue Table (join table)
referral_id (foreign key to the referral table, id column)
user_id (foreign key to the user table, id column)
EJB's
@Entity
@Table(name = "users")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private Integer id;
...
@JoinTable(name = "referral_user_queue", joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")}, inverseJoinColumns = {@JoinColumn(name = "referral_id", referencedColumnName = "id")})
@ManyToMany
private Collection
...
getters and setters
}
@Entity
@Table(name = "referral")
public class Referral implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private Integer id;
...
@ManyToMany(mappedBy = "referralIdCollection")
private List
...
getters and setters
}
The User is the owning entity
I have stateless session beans that are facades to these entities (since netbeans generates them for me). The calls I make below are simply calls that end up as "merge" and "find" nothing more. So a call to userFacade.updateUser(User user) ends up being em.merge(user) where em is the injected EntityManager in the stateless session bean.
Here's the test method (I'm using a servlet as a test client for simplicity)
public class TestReferralServlet extends HttpServlet {
@EJB
private UserFacadeLocal userFacade;
@EJB
private ReferralFacadeLocal referralFacade;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
this.moveReferral(out);
.....
}
private void moveReferral(PrintWriter out) {
//locate the referral, I just happen to have one with the
//primary key of 31
Referral referral = referralFacade.find(new Integer(31));
User me = userFacade.findUser(1);
User advisor = userFacade.findUser(3);
User drs = userFacade.findUser(5);
User counslor = userFacade.findUser(6);
out.println("
1) users size=" + referral.getUserIdCollection().size());
//you have to make a copy of the collection or you will get a
//concurrent update exception when removing from within a loop.
List
for(User u : referral.getUserIdCollection()) {
users.add(u);
}
//clean out any users and start with a fresh slate
for(User u : users) {
referral.getUserIdCollection().remove(u);
u.getReferralIdCollection().remove(referral);
userFacade.updateUser(u);
referralFacade.updateReferral(referral);
}
//grab fresh copy just to make sure everything is clean
referral = referralFacade.find(new Integer(31));
out.println("
2) users size=" + referral.getUserIdCollection().size());
//add all users to the referral
referral.getUserIdCollection().add(me);
me.getReferralIdCollection().add(referral);
referral.getUserIdCollection().add(drs);
drs.getReferralIdCollection().add(referral);
referral.getUserIdCollection().add(counslor);
counslor.getReferralIdCollection().add(referral);
referral.getUserIdCollection().add(advisor);
advisor.getReferralIdCollection().add(referral);
userFacade.updateUser(me);
userFacade.updateUser(drs);
userFacade.updateUser(counslor);
userFacade.updateUser(advisor);
referralFacade.updateReferral(referral);
//grab fresh copy to make sure everyone was really added
referral = referralFacade.find(new Integer(31));
out.println("
3) users size=" + referral.getUserIdCollection().size());
for(User u : referral.getUserIdCollection()) {
out.println("
" + u.getFirstname());
}
//now remove drs only
drs.getReferralIdCollection().remove(referral);
referral.getUserIdCollection().remove(drs);
userFacade.updateUser(drs);
referralFacade.updateReferral(referral);
//grab fresh copy to make sure only drs was removed
referral = referralFacade.find(new Integer(31));
out.println("
4) users size=" + referral.getUserIdCollection().size());
for(User u : referral.getUserIdCollection()) {
out.println("
" + u.getFirstname());
}
//voila...everything is right in the world and I didn't write any jdbc code
}
}
Just remember to update both ends of the relationship or the cache will think it still has it. That's why I'm calling userFacade.update and referralFacade.update
