Hibernate Example OneToMany with compositeKey

Question

Can you give me an example of a Hibernate mapping for the following situation:

1. Parent table(foo) with a simple primary key (foo_id)
2. child table(bar) with a composite key consisting of a> Foreign key to parent table (foo_id) b> key(item) of type string
3. There is one parent to many child
4. The Parent class will have a list of Child objects
5. When a Parent class is saved, updated, deleted the changes will cascade to the Child

Thank you

Answer 1

I haven't done exactly what you are asking for but this might start you off in the right direction. I think it should work. This page explains these annotations in greater detail.

@Entity
public class Foo {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    public Long getId(){

    }
    ...
    @OneToMany(mappedBy="foo")
    public Collection<Bar> getBars() {

    }


...
}


@Entity
@IdClass(BarPk.class)
public class Bar implements Serializable {
    @ManyToOne
    @JoinColumn(name="foo")
    @Id
    public Foo getFoo() {
        return foo;
    }

    @Column(name="key", length=255)
    @Id
    public String getKey(){

    }

}


@Embeddable
public class BarPk implements Serializable {
    public Foo getFoo() {
        return foo;
    }
    public void setFoo(Foo foo) {

    }
    public String getKey(){
    ...
    }   

    public void setKey(String key){
    ...
    }     

    //you must include equals() and hashcode()    
}

Answer 2

Can be a @Id annotation assigned to a Foo property ????

Answer 3

Yes, you should use the following mapping

@Entity public class Parent {

@Id
private Integer id;

@CollectionOfElements
@JoinTable(
    name="Child",
    joinColumn=@JoinColumn(name="PARENT_ID"))
@IndexColumn("childIndex")
private List<Child> childList = new ArrayList<Child>();

}

Notice @CollectionOfElements and IndexColumn is Hibernate specific annotations, not JPA 1.0 specification. JPA 2.0 will introduce them.

@Embeddable public class Child {

// @Embeddable class does not contains identifiers 
// child class specific property's

}

So the following code will works fine

Parent parent = new Parent();

parent.getChildList().add(new Child()); parent.getChildList().add(new Child()); // other child

session.save(parent); // A parent and two children will be saved

The drawback with this issue is that @CollectionOfElements annotation only applies to @Embeddadble class, not a Entity class. If you want a Child class as a Entity class, i would like to see the solution. It is not possible applies at the same time @Entity and @Embeddable annotations to a class.

Regards Arthur Ronald F D Garcia (Java programmer) Natal/RN - Brazil