在Spring Data JPA中获取具有子级筛选集合的父级实体列表

Question

So I've been stuck on this problem for about half a day so I am wondering if I am just over-complicating things.

My application has three different Java object classes: Grandparent, Parent, and Child. Each Grandparent contains a List of Parents, and each Parent contains a List of Children. Child has an "isWellBehaved" property, which is a boolean.

We are using Spring Data JPA and Hibernate in order to map the data to a database. Our application contains a lot of nested entities and circular relationships and we are relying on projections to keep our request size down.

The Problem: given a grandparent id, I want to return a list of all Parents (as projections). I want each of the Parents to contain a list of Child projections, but only if the Child is well behaved. The rest of the children in the collection should be filtered out from the collection.

What would be the simplest way to achieve this? We are not using Hibernate filters at the moment and I am not keen on introducing them as we are not likely to need them anywhere else (either way, would it be suited for this purpose?). I have used JPA Criteria API predicates (very little) but find it difficult to adapt that to this particular scenario. Is a native query the way to go? I've started going in that direction but am having some issues mapping all the fields to our Spring entity due to all the nested dependencies so just want to make sure I am even headed in the right direction before I continue.

My (simplified) parent entity class looks like this:

@Entity
@Table(name="parent"
public class Parent {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="parent_id")
    Integer id;

    Integer grandparentId; 

    @OneToMany(mappedBy = "parent")
    List<Child> children;
}

Child class:

@Entity
@Table(name="child"
public class Child {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="child_id")
    Integer id;

    @ManyToOne
    @JoinColumn(name="parent_id")
    Parent parent;

    boolean isWellBehaved; 
}

Parent repository interface:

@RepositoryRestResource(excerptProjection = ParentProjection.class)
public interface ParentRepository extends JpaProjectionRepository<Parent, Integer, ParentProjection> {

    List<ParentProjection> findAllByGrandparent_Id(Integer grandpaId);
}

Answer 1

As you have said:

I want each of the Parents to contain a list of Child projections, but only if the Child is well behaved.

List<childerns>allChilderns=parentsList.stream().map(parent>dao.findchildernByParentId()).collect(Collectors.List());

allChilderns.stream().filter(childern->childern.isWellBehaved()==true).collect(Collectors.toList());

1. Get all the parents by GrandParentId--the one which you are doing.
2. Once you got all the parents,for each parent findchildernByParentId.
3. and then filter out the childern on the basis of condition.

Let me know:)

Answer 2

You can use @Where annotation of hibernate on collection. It will be something like

@Entity
@Table(name="parent"
public class Parent {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="parent_id")
    Integer id;

    Integer grandparentId; 

    @Where(clause = "isWellBehaved=true")
    @OneToMany(mappedBy = "parent")
    List<Children> children;
}