为什么查询返回空集合？

Question

我有以下查询始建通过Laravel：

$res = Announcement::whereExists(function ($query) { 
       $query->select(DB::raw(1)) 
        ->from('announcement_category')->join('user_category', 'user_category.category_id', '=', 'announcement_category.category_id') 
        ->where('user_category.user_id', '=', 1) 
        ->where('announcement_category.announcement_id', '=', 'announcements.id'); 
      }); 

dd($res->get()); 

上面的代码给我空集：dd($res->get());。

此查询的普通的SQL代码：

select * from `announcements` where exists (select 1 from 
`announcement_category` inner join `user_category` on 

`user_category`.`category_id` = `announcement_category`.`category_id` where `user_category`.`user_id` = 1 

and `announcement_category`.`announcement_id` = announcements.id) 

and `announcements`.`deleted_at` is null 

如果直接在MySQL执行此，我得到两个结果行。

但是为什么dd($res->get());回廊空？

Answer 1

我不认为这是在雄辩模型whereExists ...试试这个：

$res = DB::table('announcement')->whereExists(function ($query) { 
       $query->select(DB::raw(1)) 
        ->from('announcement_category')->join('user_category', 'user_category.category_id', '=', 'announcement_category.category_id') 
        ->where('user_category.user_id', '=', 1) 
        ->where('announcement_category.announcement_id', '=', 'announcements.id'); 
      })->get();