对于返回Long值的查询，Spring IncorrectResultSizeDataAccessException？ Java的

Question

我添加了一个新的查询方法，以现有的JPA存储库，其从OrderItem的实体，以便检索一个id为Long类型：

@Transactional("order_item") 
public interface OrderItemRepository extends PagingAndSortingRepository<OrderItem, Integer> { 

    ...other queries 

    /** 
    * Retrieves the latest modification Id of order item entity 
    * 
    * @param orderItemId id 
    * @return modificationId | null if order item is not a print product 
    */ 
    @Query("select pri.modificationId from OrderItem as oi" 
      + " join oi.physicalItems as phys" 
      + " join phys.printItem as pri" 
      + " where oi.id = :orderItemId" 
      + " order by pri.modificationId desc") 
    Long findLatestmodificationIdForOrderItem(@Param("orderItemId") Integer orderItemId); 

} 

查询大部分的作品，但有时也与此错误日志中突破：

org.springframework.dao.IncorrectResultSizeDataAccessException：结果返回多个元素;嵌套的例外是javax.persistence.NonUniqueResultException：结果在 com.sun.proxy返回多个元素

$ Proxy993.findLatestModificationIdForOrderItem（来源不明）

咨询这太问题后：setMaxResults for Spring-Data-JPA annotation?

该解决方案是将方法返回类型更改为List，但htis将破坏我的合同并需要在很多地方重构。

如何限制查询总是返回一个值而不是中断？

感谢

Answer 1

请尝试举例：

@Transactional("order_item") 
public interface OrderItemRepository extends PagingAndSortingRepository<OrderItem, Integer> { 

@Query("select pri.modificationId from OrderItem as oi" 
     + " join oi.physicalItems as phys" 
     + " join phys.printItem as pri" 
     + " where oi.id = :orderItemId" 
     + " order by pri.modificationId desc") 
List<Long> findLatestmodificationIdForOrderItemQuery(@Param("orderItemId") Integer orderItemId); 

    default Long findLatestmodificationIdForOrderItem(Integer orderItemId) { 
     List<Long> result = this.findLatestmodificationIdForOrderItemQuery(orderItemId); 
     return result.get(0); 
    } 
}