JPA（Hibernate）/QueryDSL带条件的左联接不起作用

Question

user:                          booking:

    id | name    |               id | country    | user_id | price   |
    -------------|               ------------------------------------|
     1 | Alice   |                1 | Italy      | 1       | 2000    |
     2 | Bob     |                2 | France     | 1       | 2500    |
                                  3 | Spain      | 1       | 3000    |

SELECT u.*, b.* FROM user u LEFT JOIN booking b ON u.id = b.user_id AND b.price > 2000

    id | name    | id    | country    | user_id | price   |
    -------------|----------------------------------------|
     1 | Alice   | 2     | France     | 1       | 2500    |
     1 | Alice   | 3     | Spain      | 1       | 3000    |
     2 | Bob     | null  | null       | null    | null    |

@Entity
public class User {

    @Id
    private Long id;
    private String name;

    @OneToMany(cascade = ALL, fetch = EAGER, orphanRemoval = true, mappedBy = "user")
    private List<Booking> bookings;

    // getters and setters
}

@Entity
public class Booking {

    @Id
    private Long id;
    private String name;
    private Integer price;

    @ManyToOne(fetch = LAZY)
    @JoinColumn(name = "user_id")
    private User user;

    // getters and setters
}

查询DSL：

public List<User> getUsersAndBookings() {
    QUser user = QUser.user;
    QBooking booking = QBooking.booking;

    JPAQuery<User> jpaQuery = new JPAQuery(entityManager);

    List<User> result = jpaQuery.from(user).leftJoin(user.bookings, booking).on(booking.price.gt(2000)).fetchJoin().fetch();

    return result;
}

事实上，这段代码不起作用，我得到以下异常：

org.hibernate.hql.internal.ast.QuerySyntaxException: with-clause not allowed on fetched associations; use filters [select user from com.example.demo.entity.User user left join fetch user.bookings as booking with booking.price > ?1]

问题是条件子句是在on方法-on(Booking.price.>(2000))中指定的。

List<User> result = jpaQuery.from(user).leftJoin(user.bookings, booking).where(booking.price.gt(2000)).fetchJoin().fetch();

• Spring Boot 2.0.2
• Spring Data JPA 2.0.7
• Hibernate5.2.16.final
• 查询DSL 4.1.4

Answer 1

可以在where子句中使用isnull表达式获取具有空值的行。

您的查询应该如下所示：

jpaQuery.from(user)
    .leftJoin(user.bookings, booking)
    .fetchJoin()
    .where(booking.price.gt(2000).or(booking.id.isNull())).fetch();

Hibernate生成的查询：

select
user0_.id as id1_1_0_,
bookings1_.id as id1_0_1_,
user0_.name as name2_1_0_,
bookings1_.country as country2_0_1_,
bookings1_.price as price3_0_1_,
bookings1_.user_id as user_id4_0_1_,
bookings1_.user_id as user_id4_0_0__,
bookings1_.id as id1_0_0__
from
user user0_
left outer join
booking bookings1_
on user0_.id=bookings1_.user_id
where
bookings1_.id is null
or bookings1_.price>?