Construct JPA query for a OneToMany relation

Question

I\'ve those 2 entities

Class A {
    @OneToMany(mappedBy=\"a\")
    private List bs;
}

Class B {

    @ManyToOne
    private A a;

    private Stri         


        

Answer 1

First of all, I think you can learn the answer by looking at this link and search for JOIN: http://download.oracle.com/docs/cd/E11035_01/kodo41/full/html/ejb3_langref.html

Second of all, here is my approach:

@Entity
@NamedQueries({
@NamedQuery(name="A.hasBName",query="SELECT a FROM A a JOIN a.b b WHERE b.name = :name"),
@NamedQuery(name="A.dontHasBName",query="SELECT a FROM A a JOIN a.b b WHERE b.name <> :name")
})
Class A { /* as you defined */ }

In you DAO, you can make the namedquery like this:

public List findByHasBName( String name ){
    Query q = em.createNamedQuery("A.hasBName")
            .setParameter("name", name);
    try{
        return ( (List) q.getResultList());
    } catch ( IndexOutOfBoundsException e){
        return null;
    }
}