php 我将如何在 Doctrine2 中执行 MySQL count(*)？
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How would I do MySQL count(*) in Doctrine2?
提问by matthew
I have the following Doctrine2 query:
我有以下 Doctrine2 查询：
$qb = $em->createQueryBuilder()
->select('t.tag_text, COUNT(*) as num_tags')
->from('CompanyWebsiteBundle:Tag2Post', 't2p')
->innerJoin('t2p.tags', 't')
->groupBy('t.tag_text')
;
$tags = $qb->getQuery()->getResult();
When run I get the following error:
运行时出现以下错误：
[Semantical Error] line 0, col 21 near '*) as num_tags': Error: '*' is not defined.
How would I do MySQL count(*) in Doctrine2?
我将如何在 Doctrine2 中执行 MySQL count(*)？
回答by Asciiom
You should be able to do it just like this (building the query as a string):
您应该可以这样做（将查询构建为字符串）：
$query = $em->createQuery('SELECT COUNT(u.id) FROM Entities\User u');
$count = $query->getSingleScalarResult();
回答by Boris Guéry
You're trying to do it in DQL not "in Doctrine 2".
你试图在 DQL 中而不是“在 Doctrine 2”中做到这一点。
You need to specify which field (note, I don't use the term column) you want to count, this is because you are using an ORM, and need to think in OOP way.
您需要指定要计算的字段（注意，我不使用术语列），这是因为您使用的是 ORM，并且需要以 OOP 的方式思考。
$qb = $em->createQueryBuilder()
->select('t.tag_text, COUNT(t.tag_text) as num_tags')
->from('CompanyWebsiteBundle:Tag2Post', 't2p')
->innerJoin('t2p.tags', 't')
->groupBy('t.tag_text')
;
$tags = $qb->getQuery()->getResult();
However, if you require performance, you may want to use a NativeQuerysince your result is a simple scalar not an object.
但是，如果您需要性能，您可能需要使用 a，NativeQuery因为您的结果是一个简单的标量而不是一个对象。
回答by SudarP
As $query->getSingleScalarResult() expects at least one result hence throws a no result exception if there are not result found so use try catch block
由于 $query->getSingleScalarResult() 期望至少有一个结果，因此如果未找到结果则抛出无结果异常，因此请使用 try catch 块
try{
$query->getSingleScalarResult();
}
catch(\Doctrine\ORM\NoResultException $e) {
/*Your stuffs..*/
}
