你需要为多对多关系使用另一种多态方法： https://github.com/laravel/framework/blob/master/src/Illuminate/Database/Eloquent/Model.php#L805 morhpToMany 和 belongsToMany 将相关模型作为参数传递。

You need to use another polymorphic method for a many-to-many relationship: https://github.com/laravel/framework/blob/master/src/Illuminate/Database/Eloquent/Model.php#L805 morhpToMany and belongsToMany where you pass the related model as a parameter.