OneToMany and MappedBy problem

jc7442 · **Posted:** Mon Apr 03, 2006 5:40 am

Hibernate version:3.1.2

I writte 2 classes:

Code:

@Entity
public class A extends IdentifiablePE{
  
  private List<B> bs;

  @OneToMany(cascade={CascadeType.ALL},mappedBy="a")
  public List<B> getBs() {return bs;}
  public void setBs(List<B> bs) {this.bs = bs;}
}

@Entity
public class B extends IdentifiablePE {

  private A a;

  @ManyToOne
  @JoinColumn(name = "a_id")
  public A getA() {return a;}
  public void setA(A a) {this.a = a;}
}

My problem is that when I add a B instance in A, nothing is persisted !!

Code:

a.getBs().add(b);

It works fine only if i writte:

Code:

b.set(a);

That's quite disapointing. Any idea what's going wrong ?

emmanuel · **Posted:** Mon Apr 03, 2006 5:58 am

mappedBy means this side is not the owner side of the relationship ie does not trigger an assoication update in DB.
Whe updating the non managed side, you also need to update the owning side.
In hyou case I would recommend you to write a some addB() method that add the element in the collection and call b.setA() at the same time

emmanuel · **Posted:** Mon Apr 03, 2006 5:59 am

BTW this is the way it works in plain java objects (forget about persistence), you ahev to sync both sides

jc7442 · **Posted:** Mon Apr 03, 2006 8:12 am

OK, but if I writte:

Code:

a.getBs().add(new B())

and in another transaction

Code:

a.getBs().size()
=>0

My Collection is empty, it should contain the added element !

jc7442 · **Posted:** Mon Apr 03, 2006 10:46 am

I I understant properly your answer in A I should have:

Code:

public List<B> getBs() {...}
public void addB(B b) {
  getBs().add(b);
  b.setA(this);
}

My problem is that I need getBs method in order be able to use size, insert ... and other methods of List.
But I must not use add method of List directly otherwise it is a bug.I must use addB method.

It is very bug prone. IS there another solution than implementing all the sizeB, insertB methods in A ?