Question

我有两个实体Customer和Order：

@Entity
public class Customer {

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private Long id;
  .....
  @OneToMany(mappedBy="customer")
  private Set<Order> orders = new HashSet<Order>();
  .....
}

@Entity
public class Order {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    ........
    @ManyToOne()
    private Customer;
    ........
}

我要在CrudRepository中查找所有没有订单的客户。如何编写@Query？或者如何在CrudRepository接口中编写该方法？

@Repository
public interface CustomerRepository extends CrudRepository<Customer, Long>{

  findBy ......

  @Query(".......")
  find.....

}

谢谢！

Answer 1

要查询不存在的数据，必须使用left join，如下所示：

@Query("select c from Customer as c left join c.orders as orders where orders is null")

Answer 2

您需要使用empty关键字，该关键字可以与集合表达式一起使用（无需联接）。

JPQL查询应为

select c from Customer c where c.orders is empty

CrudRepository按一对多关系筛选

2 个答案: