应该将关系与属性分离。

class Seat extends Model
{
   public $appends = ['category_id'];

   /**
    * The attributes that are mass assignable.
    *
    * @var array
    */
    protected $fillable = [
        'seat_name',
        'seat_url',
        'logo_src',
    ];

    public function getCategoryIdAttribute()
    {
        return $this->categories()->pluck('id');
    }

    public function categories()
    {
        return $this->hasMany(AdSeatCategories::class);
    }

}

一个更好的解决方案使用的关系 categories 在模特的召唤下 Seat .

class Seat extends Model
{
    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */

    protected $fillable = [
        'seat_name',
        'seat_url',
        'logo_src',
    ];

    public function categories()
    {
        return $this->hasMany(AdSeatCategories::class);
    }

}

在控制器中：

$seats = Seat::with('categories:id')->get();

它看起来像你的 getCategoryIdAttribute() 是返回一个关系，当您希望它返回集合时，请务必调用 get() 这样地：

public function getCategoryIdAttribute()
{
    return $this->hasMany(AdSeatCategories::class)->get();
}

或者，您可能需要一个关系和一个属性：

public function categories()
{
    return $this->hasMany(AdSeatCategories::class);
}

public function getCategoryIdsAttribute()
{
    return $this->categories()->get()->pluck('id');
}