CrudRepository 按一对多关系过滤

Question

I have two entity Customer and 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;
    ........
}

In the CrudRepository I want to find all customers who have no orders. How can I write the @Query? Or how can I write the method in CrudRepository Interface?

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

  findBy ......

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

}

Thanks!

Answer 1

要查询不存在的数据，您必须使用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

You need to use the empty keyword, that can be used with collection expressions (no need to join).

The JPQL query would be

select c from Customer c where c.orders is empty