How can I do paging with @OneToMany collections

Question

Suppose I have a Post entity and a Comment entity and a one to many relationship:

@Entity class Post {
    ...
    @OneToMany
    List comments;
          


        

Answer 1

Is it possible to emulate dynamic paging with @OneToMany collections on top of JPA (...)

Not supported. The standard approach would be to use a JPQL query to retrieve the comments for a given post and and to use Query#setFirstResult(int) and Query#setMaxResults(int).

On my first thought, we could create a subclass of List, (...). But I don't know whether Hibernate/JPA will recognize this, or interfere with it.

It obviously won't without an heavy patch to drastically change the default behavior.

Answer 2

I think the "right" way might be more like:

@Entity
class Post {
    ...

    public GenericModel.JPAQuery getComments() {
        return Comment.find("post_id = ?", post_id);
    }
}

and then use one of the fetch methods in JPAQuery:

// fetch first page of results, 25 results per page
post.getComments().fetch(1,25);