使用Criteria Api按嵌套字段排序时缺少行

Question

I've encounterd weird behaviour of JPA (provider: EclipseLink) using order by functionality. I have TransactionData class, which has reference to CustomerData class:

@Entity
public class TransactionData {
    //...
    @ManyToOne
    @JoinColumn(name = "CUSTOMER_ID")
    private CustomerData customer;
    //...
}

@Entity
public class CustomerData {
    //...
    @Column(name = "LAST_NAME")
    private String lastName;
    //...
}

In my project, there are some specific cases, where there are transactions, which are not assigned to any customer (called non-customer transactions).

I try to get list of all registered transactions (both cusotmer transactions and non-customer transactions) and sort them by customer's last name. To acheive this I've written following Criteria Api

CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<TransactionData> criteriaQuery = criteriaBuilder.createQuery(TransactionData.class);
Root<TransactionData> from = criteriaQuery.from(TransactionData.class);
criteriaQuery.orderBy(criteriaBuilder.asc(from.get("customer").get("lastName"));
TypedQuery<TransactionData> query = entityManager.createQuery(criteriaQuery);
return query.getResultList();

I think I should get list of all transactions, of course, with those, where customer field is set to NULL value. But JPA behaviour is different, because it cut out all transactions, where reference to customer is empty.

Answer 1

from.get("customer").get("lastName") will do implicitly an INNER JOIN. If some transactions have no customer assigned then what you need is a LEFT JOIN:

Join<TransactionData , CustomerData> customer = from.join("customer", JoinType.LEFT);
criteriaQuery.orderBy(criteriaBuilder.asc(customer.get("lastName"));