php - 当 Doctrine 查询加入时，setMaxResults 不能正常工作

Question

我想编写一个 DQL 查询来选择发布并加入另一个实体。

这是我的代码:

   $dql = '
                    SELECT p , h ,t ,m 
                    FROM App:Post p 
                    LEFT JOIN p.mentions m
                    LEFT JOIN p.tags t 
                    LEFT JOIN p.file h 
                    WHERE p.user
                    IN (
                        SELECT f FROM App:User u
                        JOIN u.followers f
                        WHERE u.id = :uid
                       )
                    OR p.user = :uid ';

    $query = $this->getEntityManager()
        ->createQuery($dql)
        ->setMaxResults(5)
        ->setParameters(['uid' => $user->getId()])
        ->getArrayResult();

但问题是 setMaxResults 不限制帖子实体而是限制标签实体在 5 上。

这是我的两种结果:

1.with setMaxResults (Not work fine)

2.with setMaxResults (Work fine)

我的代码有什么问题？

Answer 1

这是在没有分页器的情况下使用 setMaxResults() 或 setFirstResult() 时原则中的预期行为。

setMaxResults() 实际上是在生成的查询中添加一个SQL LIMIT，它不仅会像您期望的那样限制根实体，还会限制查询返回的行.这意味着在连接查询时它不会执行您想要的操作。

根据 First and Max Result Items

If your query contains a fetch-joined collection specifying the result limit methods are not working as you would expect. Set Max Results restricts the number of database result rows, however in the case of fetch-joined collections one root entity might appear in many rows, effectively hydrating less than the specified number of results.

你可以做些什么来实现你想要的是使用 Paginator关于您的查询:

$query = $this->getEntityManager()
    ->createQuery($dql)
    ->setMaxResults(5)
    ->setParameters(['uid' => $user->getId()]);
$paginator = new Paginator($query, $fetchJoinCollection = true);

$c = count($paginator);
foreach ($paginator as $post) {

}

来自上面的 Paginator 文档链接:

Paginating Doctrine queries is not as simple as you might think in the beginning. If you have complex fetch-join scenarios with one-to-many or many-to-many associations using the "default" LIMIT functionality of database vendors is not sufficient to get the correct results.

另外，请注意:

By default the pagination extension does the following steps to compute the correct result:

• 使用 DISTINCT 关键字执行计数查询。
• 使用 DISTINCT 执行限制子查询以查找当前页面中的实体的所有 ID。
• 执行 WHERE IN 查询以获取当前页面的所有结果。

This behavior is only necessary if you actually fetch join a to-many collection. You can disable this behavior by setting the $fetchJoinCollection flag to false; in that case only 2 instead of the 3 queries described are executed. We hope to automate the detection for this in the future.

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