java - 如何通过使用 Criteria API 将其子实体的属性列入白名单来选择 JPA 实体？

Question

我遇到了以下假设问题:

使用Criteria API(而不是JPQL)，并给定

1. 满是用户的表格，每个用户都有多辆汽车

   @Entity 
   public class User {
       @Id 
       private Long     id;
   
       @OneToMany 
       private Set<Car> cars;
   }
   

   @Entity 
   public class Car {
       @Id 
       private Long id;
   
       private String model;
   }
   

2. A Set<String>包含汽车模型:

   Set<String> models = getThousandsOfModels();
   

How can I select the Users having at least one Car whose model is in the models Set ?

我读过很多 SO 答案，尝试了不同的方法(最有希望的似乎涉及使用 Expression<Collection<String>> 创建谓词，使用 .in() 等)但没有任何效果。

Answer 1

下面的代码起到了作用:

Set<String> models = getHundredsOfModels(); 
if (models.size()>1000) throw new TooManyResultsException(); // Oracle limit

CriteriaBuilder cb          = em.getCriteriaBuilder();
CriteriaQuery<User> cQuery  = cb.createQuery(User.class);
Root<User> user             = cQuery.from(User.class);
List<Predicate> predicates  = new ArrayList<Predicate>();

//  This lines are the trick  ------------------------------------------
Join<User, Car> usersCars   = user.join("cars", JoinType.INNER);
Predicate p                 = usersCars.<String>get("model").in(models);
// ---------------------------------------------------------------------    

predicates.add(p);
cQuery.select(user).where(predicates.toArray(new Predicate[predicates.size()]));