Eager loading不能正常工作

Question

如果我沒有弄錯，急切加載的目的是減少數據庫查詢的數量。但是，如果我下面添加到我的查詢生成器的實例，它會爲每個記錄額外的SQL查詢返回：

 ->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(); 
      } 

它這樣做是有或無連接語句。

所以我錯過了急於加載的點，還是我做錯了？

我的第二個（稍微不相關的）問題是，如果我包含註釋 - > select（）語句，則由於某種原因，此子查詢不會生成任何結果。

事實上，Laravel正在爲每條記錄生成相同的SQL查詢。如果有兩個筆記本電腦的結果，我得到兩個相同的查詢拉第一撥出記錄每個：

 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 

這些查詢是相同的！

Answer 1

由於執行它的子查詢的末尾有get()，因此會生成多個查詢。您不會在Laravel中執行子查詢，因爲它們將在第一個查詢運行以附加關係後執行。用take(1)代替，機智將解決您的N + 1問題。