Hibernate 如何使用JPA Criteria Builder编写查询（包括子查询和exists）

正在努力使用JPA编写以下查询

Oracle查询：

Select * from table1 s
where exists (Select 1 from table2 p
              INNER JOIN table3 a ON a.table2_id = p.id
              WHERE a.id = s.table3_id
              AND p.name = 'Test');

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另外，您是否想指出一些用JPA编写复杂查询的好教程。

您可以使用JPA查询或HQL而不是Criteria Builder更简单：

从Entity1中选择e1作为e1 哪里有 从Entity2中选择e2作为e2并将e2.e3作为ent3 其中ent3.id=e1.id和e2.name='Test'

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我将使用JpaRepository、JpaSpecificationExecutor、CriteriaQuery、CriteriaBuilder回答简单汽车广告领域广告、品牌、模型的示例：

品牌[一对多]模式 模型[一对多]广告 实体：

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我理解，但要求是使用criteria Builder：criteria Builder有其自身的局限性，因此最好根据情况将其与查询相结合。不要试着用螺丝刀钉钉子，这会让你在困难中变得轻松。嗨，这是一个很好的例子。当您执行brand.setId时。。。我找不到criteria.getValue的来源。它应该是this.brandId成员变量吗？哇，我刚刚把它转换成强类型。我的org.springframework.data.jpa.domain.Specification使用通过创建import javax.persistence.metamodel.SingularAttribute实现的强类型；以及MyObject_uu类中的@javax.persistence.metamodel.StaticMetamodelMyObject.class。唷！这是一个很大的伏都教让它工作。感谢这个例子，它让我从地面！

@Entity
public class Brand {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;
  private String name;
  @OneToMany(mappedBy = "brand", fetch = FetchType.EAGER)
  private List<Model> models;
}

@Entity
public class Model {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;
  private String name;
  @ManyToOne
  @JoinColumn(name = "brand_id")
  private Brand brand;
}

@Entity
public class Advert {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;
  @ManyToOne
  @JoinColumn(name = "model_id")
  private Model model;
  private int year;
  private int price;
}

public interface AdvertRepository
  extends JpaRepository<Advert, Long>, JpaSpecificationExecutor<Advert> {
}

public class AdvertSpecification implements Specification<Advert> {
  private Long brandId;

  public AdvertSpecification(Long brandId) {
    this.brandId = brandId;
  }

  @Override
  public Predicate toPredicate(Root<Advert> root,
                               CriteriaQuery<?> query,
                               CriteriaBuilder builder) {

    Subquery<Model> subQuery = query.subquery(Model.class);
    Root<Model> subRoot = subQuery.from(Model.class);

    Predicate modelPredicate = builder.equal(root.get("model"), subRoot.get("id"));

    Brand brand = new Brand();
    brand.setId(brandId);
    Predicate brandPredicate = builder.equal(subRoot.get("brand"), brand);

    subQuery.select(subRoot).where(modelPredicate, brandPredicate);
    return builder.exists(subQuery);
  }
}

select advert0_.id as id1_0_,
       advert0_.model_id as model_id5_0_,
       advert0_.price as price3_0_,
       advert0_.year as year4_0_
from advert advert0_
where exists (select model1_.id from model model1_
              where advert0_.model_id=model1_.id
              and model1_.brand_id=?)