如何为QueryDSL中的多对多关系创建谓词BooleanExpression

问题描述

如何使用谓词BooleanExpression对多对多关系进行内部联接?

How can inner join be done on Many to Many relations using Predicate BooleanExpression?

我有2个实体

public class A {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer id;

 @ManyToMany(fetch = FetchType.LAZY,
  cascade = { CascadeType.DETACH, CascadeType.MERGE,
      CascadeType.REFRESH, CascadeType.PERSIST})
  @JoinTable(name = "a_b_maps",
      joinColumns = @JoinColumn(name = "a_id", nullable =
          false,referencedColumnName = "id"),
      inverseJoinColumns = @JoinColumn(name = "b_id", nullable = false,
        referencedColumnName = "id")
  )
  private Set<B> listOfB = new HashSet<B>();
}


public class B {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer id;

 @ManyToMany(fetch = FetchType.LAZY,
  cascade = { CascadeType.DETACH, CascadeType.MERGE,
      CascadeType.REFRESH, CascadeType.PERSIST})
  @JoinTable(name = "a_b_maps",
      joinColumns = @JoinColumn(name = "b_id", nullable =
          false,referencedColumnName = "id"),
      inverseJoinColumns = @JoinColumn(name = "a_id", nullable = false,
        referencedColumnName = "id")
  )
  private Set<A> listOfA = new HashSet<A>();
}

基本仓库

@NoRepositoryBean
public interface BaseRepository<E, I extends Serializable>
    extends JpaRepository<E, I> {

}

以及A的存储库类

public interface Arepo extends BaseRepository<A, Integer>,
    QueryDslPredicateExecutor<A> {
    Page<A> findAll(Predicate predicate, Pageable pageRequest);

}

现在，我想将A Repo与Predicate查询一起使用.我需要形成一个谓词，在其中我可以根据一些给定的B加载A

Now I want to use A Repo with Predicate query. I need to form a predicate where I can load A based on some given Bs

我尝试过

QA a = QA.a;
QB b = QB.b;
BooleanExpression boolQuery = null;
JPQLQuery<A> query = new JPAQuery<A>();
  query.from(a).innerJoin(a.listOfB, b)
    .where(b.id.in(someList));

现在我可以形成一个JPQLQuery，但是存储库需要一个谓词.如何从JPQLQuery获取谓词?

Now I am able to form a JPQLQuery, but the repository expects a Predicate. How can I get Predicate from the JPQLQuery??

或者，如何使用谓词实现内部联接?

Or, how can the inner join be achieved using Predicate?

推荐答案

借助此处给出的答案，我能够创建谓词

I am able to create a Predicate with the help of answer given here

https://stackoverflow.com/a/23092294/1969412 .

SO，我直接使用

a.listOfB.any()
      .id.in(list);

这就像一种魅力.

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