php - Laravel:在急切加载中将类函数作为回调传递？

Question

我使用 constraint eager load使用匿名函数:

$users = App\User::with(['posts' => function ($query) {
    $query->where('title', 'like', '%first%');
}])->get();

现在我想用类函数替换匿名函数。根据PHP: How to use a class function as a callback我找到了

A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.

因此我预计以下内容会起作用:

public function start()
{
   $users = App\User::with(['posts' => [$this, 'addRestrain']])->get();
   // ...
}

private function addRestrain($query)
{
  $query->where('title', 'like', '%first%');
}

然而，Laravel 检测到传递的参数不是一个闭包，而是一个数组:

"Type error: Argument 3 passed to Illuminate\Database\Eloquent\Builder::eagerLoadRelation() must be an instance of Closure, array given, called in

这是否意味着不能将类函数用于预加载约束？

Answer 1

从 PHP 7.1.0 开始，您可以使用 Closure::fromCallable ( docs ):

$users = App\User::with(
  [ 'posts' => \Closure::fromCallable([$this, 'addRestrain']) ]
)->get();

否则，您只能使用匿名函数包装 $this->addRestrain 调用。