Question

Hy all,
I have three tables Child, Pet and Toy. Pet has a reference key the child id, and a toy has a reference key to a dog id.
I want to load all data about a Child and his pets, but i don’t want to load the toy data

@OneToMany(mappedBy = "petEntity", fetch = FetchType.LAZY)
public Set<PetEntity> getPetEntitySet() {
    return petEntitySet;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "ChildId", insertable = false, updatable = false)
public ChildEntity getChildEntity() {
    return childEntity;
}

same for set of toys.

to load data i have

List<ChildEntity> list = entityManager.createQuery(
"SELECT c FROM ChildEntity c "+
"LEFT JOIN FETCH c.petEntitySet ",
 ChildEntity.class).getResultList();
    return list;

but this thing loads me all data, not just the information about child and his pets.

How can i suppress the entity manager to load only the data in the table, and not to make joins when i don’t want that

Thanks for your advices

i forgot to mention that in this chase it doesn’t only load all data, but it returns more than just one copy of a child elemnt

Answer 1

The reason why it is loading more data is because you are using the keyword fetch. This will EAGERLY load whatever the child’s pets.
Just remove the fetch and lazy loading will occur.

Update

I see that this is actually what you want, so just ensure equals() and hashCode() is correctly overriden in all relevant classes, as I assume you are using Set.

In this way, jpa knows how to look for duplicates

Second update

Yes you can easily use DISTINCT in your queries.

Just add DISTINCT in your select

List<ChildEntity> list = entityManager.createQuery(
"SELECT DISTINCT c FROM ChildEntity c "+
"LEFT JOIN FETCH c.petEntitySet ",
 ChildEntity.class).getResultList();
    return list;