Question

Here is my code

@Entity
class Parent extends Person {
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true, mappedBy = "father")
    private List<Child> children;

    // ...

    public void addChild(Child c) {
        children.add(c);
    }

}

@Entity
class Child extends Person {
    @ManyToOne(cascade=CascadeType.ALL)
    @JoinColumn(name = "id")
    private Parent father;

    public Child() {
        this(NoParent.getInstance());//
    }

    public Child(Parent p) {
        super();
        setParent(p);
    }

    // ...
}

@MappedSuperclass
class Person {
    @Id
    private Integer id;
    private String name;
}

class MyParentService {

    public void addChild(String name, Parent parent) {
        Child c = new Child(parent);
        c.setName(name);
        parent.addChild(c);

        em.getTransaction.begin();
        em.merge(parent);
        em.getTransaction.commit();// Here two children with same name but different ids are created ...
    }
}    

Each time I run it, two children are added to the database while I just want one !
What am I doing wrong ?

Java 6
JPA 2
Hibernate 3.6.8.GA

Answer 1

I read the Hibernate documentation which is really confusing and didn’t help me much.

Notice, I have found that ObjectDB had recently faced AND fixed the exact same bug.
(Hibernate guys why are you waiting for so long ??)

Nevertheless, here the solution I came up with :

STEP 1:
Create a fresh new child (ie in detached state) and call its setParent method to link to its parent.

STEP 2:
Persist this child.

STEP 3:
Make changes to child as you need and merge it later.

The solution is quite no elegant, but it works !
Next you’ll fetch your parent object, it will have the previously child(ren) linked to it manually.