Can you control fetching behaviour in Hibernate using the criteria API?

Question

I know you can control fetching behaviour using @javax.persistence.FetchType, however can you control the fetching programmatically from within a JPA Criteria query? Basically I can tell from the query what part of the application is likely calling and what part of the model will (most likely) be needed.

I couldn't find an answer in any of the tutorials but these old questions:

NHibernate manually control fetching which is about NHibernate and has non-answers
How do you programmatically turn off eager fetching with hibernate? which doesn't mention the criteria API, and is so ancient as not to make this question an automatic duplicate, however I suspect the answer may still be the current situation.
JPA & Criteria API - Select only specific columns which is about returning tuples and not the model itself

tl;dr: can you control the fetching programmatically from within a JPA Criteria query?

you mean, like an EntityGraph? which applies to JPQL or Criteria — Neil Stockton, Dec 07 '15 at 16:22

score 2 · Accepted Answer · answered Dec 07 '15 at 17:30

You can use entity graphs for this (which works with JPQL and Criteria API).

Example:

@Entity
@NamedEntityGraph(name = "User.withRoles", attributeNodes = {
    @NamedAttributeNode("roles") // fetch "roles" eager
})
@NamedQuery(name = "User.byName", query = "SELECT u FROM User u WHERE u.name = :name")
public class User {
    /* ... */

    @Column(updatable = false)
    private String name;

    @ManyToMany // fetch lazy by default
    @JoinTable(name = "user_role", /* ... */)
    private Set<Role> roles;
}

public User getUser(String name, boolean withRoles) {
    TypedQuery<User> query = entityManager.createNamedQuery("User.byName", User.class);
    if (withRoles) {
        EntityGraph<User> loadGraph = (EntityGraph<User>) entityManager.createEntityGraph("User.withRoles");
        query.setHint("javax.persistence.loadgraph", loadGraph);
    }

    try {
        return query.setParameter("name", name).getSingleResult();
    } catch (NoResultException ex) {
        return null;
    }
}

Similarly you can also use a fetch graph to exclude fields from being fetched.

@Neil exactly. Didn't see your comment at the time. :) – jabu.10245 Dec 07 '15 at 18:15 — jabu.10245, Dec 07 '15 at 18:15

Can you control fetching behaviour in Hibernate using the criteria API?

1 Answers1