JPQL和JPQL构造函数表达式中的子查询

Question

我有一个表ROOT和一个包含与ROOT相关行的表子级。

我想为根的每一行检索一个对象，该对象包含根对象以及与CHILDREN表中的ROOT.id相关的行数。

这可以很容易地在SQL中实现，但我想知道如何在JPQL中编写

在SQL中：

SELECT 
    r.*, 
    (SELECT COUNT(c.i_id) 
     FROM 
        children c 
    WHERE 
        c.rootId = r.id)
FROM root r;

Caused by: org.hibernate.HibernateException: Errors in named queries: xxx
Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: Unable to locate 
           appropriate constructor on class RootExtended...

package plop;

public class RootExtended{

    private Root root;

    private Long count;

    public RootExtended(final Root root, final Long count) {
        this.root= root;
        this.count= count;
    }

    // getters and setters to follow
}

SELECT 
    new plop.RootExtended(r, 
                    (SELECT 
                         count(c.id) 
                     FROM 
                         Child as c 
                     WHERE 
                         c.rootId = r.id
                     )
                    ) 
FROM 
    Root as r 

知道吗？

Answer 1

public class RootExtended{

private Root root;

private Long count;

public RootExtended(final Root root, final Long count) {
    this.root= root;
    this.count= count;
}

// getters and setters to follow
}

SELECT NEW package.RootExtended ( rt.r, rt.cnt) from ( select r from Root r, 
      (SELECT count(c.id) as cnt FROM Child c  WHERE  c.rootId = r.id ) rt )