JPA 2 + Criteria API - 定义子查询

Question

我尝试将SQL查询转换为Criteria API，但目前为止没有成功。我可以创建两个单独的查询来返回我需要的值，但我不知道如何将它们合并到一个查询中。

这里是sql语句，其工作原理：

select company.*, ticketcount.counter from company 
    join 
(select company, COUNT(*) as counter from ticket where state<16 group by company) ticketcount 
on company.compid = ticketcount.company; 

此条件查询返回内部查询结果：

CriteriaBuilder cb = em.getCriteriaBuilder(); 
CriteriaQuery<intCompany> qTicket = cb.createQuery(intCompany.class); 
Root<Ticket> from = qTicket.from(Ticket.class); 
Path groupBy = from.get("company");   
Predicate state = cb.notEqual(from.<State>get("state"), getStateById(16));   
qTicket.select(cb.construct(
    intCompany.class, cb.count(from),from.<Company>get("company"))) 
     .where(state).groupBy(groupBy);     
em.createQuery(qTicket).getResultList(); 

在我定义了一个小包装/辅助类应用：

public class intCompany{ 
    public Company comp; 
    public Long opentickets; 
    public intCompany(Long opentickets,Company comp){ 
     this.comp = comp; 
     this.opentickets = opentickets; 
    } 
    public intCompany(){ 

    } 
} 

那么有没有人有一个想法如何得到这个工作？

更新

谢谢。我按照您的建议更改了标准查询。我只需要在最后添加一个循环来获取我想要的信息。

List<intCompany> result = em.createQuery(cq).getResultList(); 
List<Company> cresult = new ArrayList(); 
    for(intCompany ic: result){ 
     ic.comp.setOpentickets(ic.opentickets.intValue()); 
     cresult.add(ic.comp); 
    } 
return cresult; 

也许这是不可能的原始SQL转换为Criteria API。

另一个更新

我想通了，我不得不把原来的SQL表达式更改为

select company.*, ticketcount.counter from company 
    left join 
(select company, COUNT(*) as counter from ticket where state<16 group by company) ticketcount 
on company.compid = ticketcount.company; 

否则我不明白公司与中票表中没有条目。

那么还有其他建议吗？

Answer 1

你几乎完成了一切。

//---// 
CriteriaBuilder cb = em.getCriteriaBuilder(); 
//Your Wrapper class constructor must match with multiselect arguments 
CriteriaQuery<IntCompany> cq = cb.createQuery(IntCompany.class); 
//Main table 
final Root<Ticket> fromTicket= cq.from(Ticket.class); 
//Join defined in Ticket Entity 
final Path company = fromTicket.get("company"); 
//Data to select 
cq.multiselect(cb.count(from), company); 
//Grouping 
cq.groupBy(company); 
//Restrictions (I don't really understand what you're querying) 
Predicate p = cb.lessThan(fromTicket.get("state"), 16); 
//You can add more restrictions 
// p = cb.and/or(p, ...); 
cq.where(p); 
List<IntCompany> results = entityManager.createQuery(cq).getResultList(); 

这应该按预期工作。

Answer 2

我有类似的问题。我的解决方案是使用左外连接。

CriteriaBuilder cb = entityManager.getCriteriaBuilder(); 
CriteriaQuery<Entity> query = cb.createQuery(Entity.class); 
Root<Entity> root = query.from(Entity.class); 

Join<Entity,ChildEntity> join = root.join(Entity_.children, JoinType.LEFT); 
query.groupBy(root.get(Entity_.id)); 
query.select(
    cb.construct(
    EntityDTO.class, 
    root.get(Entity_.id), 
    root.get(Entity_.name), 
    cb.count(join) 
)); 

这JoinType.LEFT保证你会得到实体记录（公司），即使它不具有任何的子实体（门票）。

实体类：

@Entity 
public class Entity { 
    ... 

    @OneToMany(targetEntity = ChildEntity.class, mappedBy = "parent", fetch = FetchType.LAZY, orphanRemoval = false) 
    private Set<ChildEntity> objects; 

    ... 
} 

静态模式：

@StaticMetamodel(Entity.class) 
public class Entity_ { 
    public static volatile SingularAttribute<Entity, Long> id; 
    public static volatile SingularAttribute<Entity, String> name; 
    ... 
    public static volatile SetAttribute<Entity, ChildEntity> objects; 
}