Laravel 使用 morphMany 关联删除无法执行模型事件

cases删除记录后，cases_media和attachment都删除对应的关联记录，可是attachment的模型事件无法执行。

Cases::find(id)->delete();

模型Cases

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Support\Facades\Storage;

class Cases extends Model
{
    protected $table = 'cases';
    protected $guarded = [];
    protected $primaryKey = 'id';

    protected $casts
        = [
            'public' => 'boolean'
        ];

    public static function boot()
    {
        parent::boot();

        static::deleted(function ($cases) {
            $cases->medias()->delete();
            $cases->attachments()->delete();
        });
    }

    /**
     * 媒体资源
      * @return \Illuminate\Database\Eloquent\Relations\HasMany
     */
     public function medias()
     {
         return $this->hasMany('App\Models\CasesMedia')->orderBy('id', 'desc');
    }

    /**
     * 附件表信息
      * @return \Illuminate\Database\Eloquent\Relations\MorphMany
     */
    public function attachments()
    {
        return $this->morphMany('App\Models\Attachment', 'model');
    }
}

附件模型Attachment

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Support\Facades\Storage;
use Illuminate\Support\Facades\Log;

class Attachment extends Model
{
    protected $table = 'attachments';
    protected $guarded = [];

    public static function boot()
    {
        parent::boot();

        // 删除文件
        static::deleting(function ($attachment) {
        // 这里无法执行
            Storage::disk($attachment->disk)->delete($attachment->file_path);
            Log::info($attachment->file_path);
        });
    }

    /**
     * 关联模型
     * @return \Illuminate\Database\Eloquent\Relations\MorphTo
     */
    public function model()
    {
        return $this->morphTo();
    }


}