@Batchsize 注释不适用于 OneToMany

Question

我有以下类并且在注释 @BatchSize 注释时它不起作用，我收到 n+1 select 查询。

Class Shipment{
 @OneToMany(fetch = FetchType.LAZY, mappedBy = order.shipment, cascade = CascadeType.ALL, 
 orphanRemoval = true)
 @BatchSize(size=20)
 Set<Orders> orders = new Hashset(); <---- Batch size annotation not working 
 }

Order.class

class Order{
 @ToString.Exclude
 @ManyToOne
 @JoinColumn(name = "item_fk")
 Item item;

 @ToString.Exclude
 @ManyToOne
 @JoinColumn(name = "shipment_fk")
 Shipment shipment; }

Item.class

class Item{
 String id;
 String name;
}

我收到 n+1 个查询的实现有什么错误？

Answer 1

尝试使用 List<Orders> 而不是 Set<Orders>。
请注意 documentation:

However, although @BatchSize is better than running into an N+1 query issue, most of the time, a DTO projection or a JOIN FETCH is a much better alternative since it allows you to fetch all the required data with a single query.

Answer 2

您的 N+1 查询问题是由于您在 Order 中急切获取 Item。在那里更改为 LAZY，您应该可以开始了。

@Batchsize 注释不适用于 OneToMany

@Batchsize annotation not working for OneToMany

orm

hibernate

jpa

hibernate-mapping

spring-boot