弹簧数据 JPA.子实体的分页

Spring Data JPA. Pagination for child entities(弹簧数据 JPA.子实体的分页)

问题描述

我将 Spring Data JPA 与 Spring Boot 版本 1.3.6.RELEASE 与内存数据库一起使用.

I'm using Spring Data JPA with Spring boot version 1.3.6.RELEASE with in-memory database.

我想知道如何从父实体对子实体进行分页.将 fetch 设置为 LAZY 对我来说不是解决方案.

I'm wondering how to paginate the child entities from a parent entity. Setting fetch to LAZY is not a solution for me.

这是用例:

1. Parent 与 Childentity 具有单向 oneToMany 关系.
2. 一个Parent的Child数量可以达到100,000(LAZY不是解决办法)
3. 我不想让所有孩子进行分页(出于 CPU 和内存原因)

1. Parent has an unidirectional oneToMany relation with Child entity.
2. The number of Child for one Parent can reach 100,000 (LAZY is not a solution)
3. I don't want to fetch all the child to do the pagination (For CPU and Memory reason)

这是一个代码示例:

@Entity
public class Parent{
    @Id
    private Integer id;

    @OneToMany
    private List<Child> childs;
}

@Entity
public class Child {
    @Id
    private Integer id;
}

public interface ParentRepository extends JpaRepository<Parent, Integer>{}
public interface ChildRepository extends JpaRepository<Child, Integer>{}

我在父存储库中尝试过此操作失败:

I've tried this in the Parent repository unsuccessfully :

Page<Child> findById(int id, Pageable pageable);

这将返回父实体，而不是子实体.

This returns a Parent entity, not a Child entity.

知道怎么做吗?

推荐答案

下面是一个代码示例，可以获取知道父实体的子实体.请注意，此查询将返回 Child 的分页结果.

Here is a sample of code that can fetch the child entities knowing the parent. Note that this query will return a paginated result of Child.

 /**
  * Find Child entities knowing the Parent.
  */
  @Query("select child from Parent p inner join p.childs child where p = :parent")
  public Page<Child> findBy(@Param("parent") Parent parent, Pageable pageable);

你可以这样使用它:

Page<Child> findBy = repo.findBy(parent, new PageRequest(page, size));

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