Eager loading不能正常工作

如果我没有弄错，急切加载的目的是减少数据库查询的数量。但是，如果我下面添加到我的查询生成器的实例，它会为每个记录额外的SQL查询返回：Eager loading不能正常工作

 ->with([ 
      'firstEarmark' => function($q) { 
       $q 
       ->select('earmarks.*') 
       ->join('locations', 'locations.id', '=', 'earmarks.location') 
       ->select('earmarks.*', 'locations.location AS earmarked_location') 
       ->where('date', '>=', date('m/d/Y'))->orderBy('date', 'asc') 
       ->get(); 
      }

它这样做是有或无连接语句。

所以我错过了急于加载的点，还是我做错了？

我的第二个（稍微不相关的）问题是，如果我包含注释 - > select（）语句，则由于某种原因，此子查询不会生成任何结果。

事实上，Laravel正在为每条记录生成相同的SQL查询。如果有两个笔记本电脑的结果，我得到两个相同的查询拉第一拨出记录每个：

 113 Prepare select `earmarks`.*, `locations`.`location` as `earmarked_location` from `earmarks` inner join `locations` on `locations`.`id` = `earmarks`.`location` where `earmarks`.`laptop_id` in (?, ?) and `date` >= ? order by `date` asc 
     113 Execute select `earmarks`.*, `locations`.`location` as `earmarked_location` from `earmarks` inner join `locations` on `locations`.`id` = `earmarks`.`location` where `earmarks`.`laptop_id` in (1, 2) and `date` >= '11/04/2016' order by `date` asc 
     113 Close stmt  
     113 Prepare select `earmarks`.*, `locations`.`location` as `earmarked_location` from `earmarks` inner join `locations` on `locations`.`id` = `earmarks`.`location` where `earmarks`.`laptop_id` in (?, ?) and `date` >= ? order by `date` asc 
     113 Execute select `earmarks`.*, `locations`.`location` as `earmarked_location` from `earmarks` inner join `locations` on `locations`.`id` = `earmarks`.`location` where `earmarks`.`laptop_id` in (1, 2) and `date` >= '11/04/2016' order by `date` asc

这些查询是相同的！

来源

2016-11-04 daninthemix

由于执行它的子查询的末尾有get()，因此会生成多个查询。您不会在Laravel中执行子查询，因为它们将在第一个查询运行以附加关系后执行。用take(1)代替，机智将解决您的N + 1问题。

来源

2016-11-04 17:04:14

Eager loading不能正常工作

回答

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