java - HQL 按表达式排序

Question

我有两个持久类，Comment 和 Vote。一个 Comment 可以与多个 Vote 相关联，并且它们之间存在 @OneToMany - @ManyToOne 关系正常工作。我想做的是按最多赞成票对评论进行排序。如果 Vote.up 列为 1，则 Vote 为赞成票；如果 Vote.up 为 ，则为反对票0。我正在尝试找出它们的区别

到目前为止，这是我的 HQL，但它不工作

select c from Comment c
order by (
    (select count(*) from c.votes v where v.up = 1) 
    - (select count(*) from c.votes v where v.up = 0)
) desc

有办法吗？

Answer 1

HQL 不支持这种语法，因此您必须为此使用 native 查询:

List<Comment> comments = (List<Comment>) session.createSQLQuery(
        "select * " +
        "from Comment " +
        "where id in (   " +
        "    select comment_id " +
        "    from (     " +
        "        select        " +
        "            c.id as comment_id,        " +
        "            SUM(CASE WHEN v.up=1 THEN 1 ELSE -1 END) AS vote_count     " +
        "        from Comment c     " +
        "        left join Votes v on c.id = v.comment_id     " +
        "        group by comment_id     " +
        "        order by vote_count desc   " +
        "    ) c_v " +
        ") c_id"
).addEntity(Comment.class).list();