CrudRepository 按一對多關系過濾

Question

我有兩個實體客戶和訂單：

@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;
    ........
}

在CrudRepository我想找到所有沒有訂單的客戶。 我該如何編寫@Query？ 或者如何在 CrudRepository 接口中編寫方法？

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

  findBy ......

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

}

謝謝！

Answer 1

要查詢不存在的數據，您必須使用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

您需要使用可與集合表達式一起使用的empty關鍵字（無需加入）。

JPQL 查詢將是

select c from Customer c where c.orders is empty