EntityManager通过joinColumn查询

Question

我有一个Login实体和一个Customer实体.Login.username是customer表中的外键.因此Java CustomerPOJO中的以下行

@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "username", nullable = false)
private Login login;

我的问题是:有没有一种简单的方法来查询customer表使用username？还是必须我第一次取login的username,然后customer用login？

这是JPA条件查询.而且,是的,我更愿意使用条件查询.

public Customer getCustomerByUsername(String username) throws EntityNotFoundException {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Customer> criteriaQuery = criteriaBuilder.createQuery(Customer.class);
    Root<Customer> root = criteriaQuery.from(Customer.class);
    Path<String> path = root.<String>get("username");
    criteriaQuery.where(criteriaBuilder.equal(path, username));
    return entityManager.createQuery(criteriaQuery).getSingleResult();
}

这条线Path<String> path = root.<String>get("username")正在抛出一个例外username ... is not present.

Answer 1

使用JPQL的正确解决方案是

Query q = entityManager.createQuery("SELECT c FROM Customer c WHERE c.login.username = :username");
    q.setParameter("username", username);
    return (Customer) q.getSingleResult();