JPA: How to get entity based on field value other than ID?

Question

In JPA (Hibernate), when we automatically generate the ID field, it is assumed that the user has no knowledge about this key. So, when obtaining the entity, user would query

Answer 1

Basically, you should add a specific unique field. I usually use xxxUri fields.

class User {

    @Id
    // automatically generated
    private Long id;

    // globally unique id
    @Column(name = "SCN", nullable = false, unique = true)
    private String scn;
}

And you business method will do like this.

public User findUserByScn(@NotNull final String scn) {
    CriteriaBuilder builder = manager.getCriteriaBuilder();
    CriteriaQuery criteria = builder.createQuery(User.class);
    Root from = criteria.from(User.class);
    criteria.select(from);
    criteria.where(builder.equal(from.get(User_.scn), scn));
    TypedQuery typed = manager.createQuery(criteria);
    try {
        return typed.getSingleResult();
    } catch (final NoResultException nre) {
        return null;
    }
}