当使用多对多关系Laravel / Eloquent / Query构建器时，如何从另一个表中获取所有书籍
问题描述：
Let me explain the scenario.
i have tables:
competitions
id title body
then
books
id name user_id
then i have a pivot table to store participants
so
participants
id competition_id user_id
Now i have set some relationships for these models.
Competition model
public function participants()
{
return $this->belongsToMany('App\User');
}
User model
public function participatedCompetitions()
{
return $this->belongsToMany('App\Competition');
}
Now i am fetching one single competition and in that same query i need to fetch a list of books of the participants of that competition. So how can i achieve this. Thanks.
答
Here is how you get all the books:
$userIds = $competition->participant()->get()->pluck('id');
// $userIds is your collection of User Ids that is participant in that compititions.
$books = Book::whereIn('user_id',$userIds)->get();