如何对多对多数据表 followers 使用模型观察事件？$this->followings ()->sync ($user_ids, false) 无法触发 created?

通过user_user构建了数据表followers，models里也有follower，但是对Follower使用Observer事件无效。

<?php

namespace App\Observers;

use App\Models\Follower;

// creating, created, updating, updated, saving,
// saved,  deleting, deleted, restoring, restored

class FollowerObserver
{
    public function created(Follower $follower)
    {
        $user = $follower->user;
        $user->increment('follower_count', 1);

        $user = $follower->follower_user;
        $user->increment('following_count', 1);
    }

    public function deleted(Follower $follower)
    {
        $user = $follower->user;
        $user->increment('follower_count', -1);

        $user = $follower->follower_user;
        $user->increment('following_count', -1);
    }

}

    public function follow($user_ids)
    {
        if (!is_array($user_ids)) {
            $user_ids = compact('user_ids');
        }
        $this->followings()->sync($user_ids, false);
    }

    public function unfollow($user_ids)
    {
        if (!is_array($user_ids)) {
            $user_ids = compact('user_ids');
        }
        $this->followings()->detach($user_ids);
    }