EntityManager query by joinColumn

entitymanager, java, joincolumn, jpa

Solution

The correct solution with JPQL is

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

Problem

I have a `Login` entity and a `Customer` entity. `Login.username` is a foreign key in the customer table. Hence the following line in the Java `Customer` POJO ``` @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "username", nullable = false) private Login login; ``` My question is this: Is there a simple way to query the `customer` table using `username`? Or must I first fetch `login` by `username` and then `customer` by `login`? Here is the JPA criteria query. And, yes, I would prefer to use criteria query. ``` 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(); } ``` The line `Path<String> path = root.<String>get("username")` is throwing an exception saying that `username ... is not present.`

Original source