DQL OneToMany 查询和执行平均

Question

在实体之间的 OneToMany 关系中：

Composer > Soundtrack
Soundtrack > SoundtrackRating

我想 select 每个 Soundtrack 一个给定的 Composer 并为每个 Soundtrack.

平均 SoundtrackRatings

在DQL中：

SELECT s.name, (SUM(r.rating)/COUNT(r.rating)) AS rating 
FROM Soundtrack AS s 
LEFT JOIN SoundtrackRating AS r 
WHERE s.composer = :composer AND r.soundtrackId = s.id 
GROUP BY s.id 
ORDER BY rating DESC

然后我将传递类型为 Composer:

的 :composer 实例

$em->createQuery($dql)
  ->setParameter('composer', $composer)
  ->getResult();

但是在查询结果中我得到了所有 Soundtrack 条目，无论我作为参数传递什么 $composer。唯一的区别是只对给定 $composer 的评分取平均值，其余取平均值 0。

这个查询哪里有问题？

Answer 1

想通了。从 WHERE 子句中删除 r.soundtrackId = s.id 并在 LEFT JOIN 中使用 WITH 代替：

SELECT s.name, (SUM(r.rating)/COUNT(r.rating)) AS rating 
FROM Soundtrack AS s 
LEFT JOIN SoundtrackRating AS r WITH r.soundtrackId = s.id
WHERE s.composer = :composer 
GROUP BY s.id 
ORDER BY rating DESC

DQL OneToMany 查询和执行平均

DQL OneToMany query and performing average

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