Spring Data JPA.对子实体的分页 [英] Spring Data JPA. Pagination for child entities

问题描述

我正在将Spring Data JPA与Spring引导版本1.3.6一起使用，并将其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. 将获取设置为 LAZY 并不是我的解决方案.

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. 父母与孩子实体具有单向 oneToMany关系.
2. 一个 Parent 的 Child 的数量可以达到100,000(LAZY不是解决方案)
3. 我不想让所有孩子去做分页(出于CPU和内存的原因)

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>{}

我没有在父存储库中尝试过此操作:

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.

任何想法如何做到这一点?

Any idea how to do this ?

推荐答案

此处是示例代码，可以获取知道父级的子级实体. 请注意，此查询将返回分页的Child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);

您可以像这样使用它:

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

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