保存多对多关系，同步/附加不存在

我有两个以下 2 个多对多关系的模型：

use Illuminate'Database'Eloquent'Model;
class Permission extends Model
{
    /**
     * The database table used by the model.
     *
     * @var string
     */
    protected $table = 'permissions';
    /*
    |--------------------------------------------------------------------------
    | Relationship Methods
    |--------------------------------------------------------------------------
    */
    /**
     * many-to-many relationship method
     *
     * @return QueryBuilder
     */
    public function roles()
    {
        return $this->belongsToMany('App'Admin'Role');
    }
}

和

class Role extends Model
{
    /**
     * The database table used by the model.
     *
     * @var string
     */
    protected $table = 'roles';
    /*
    |--------------------------------------------------------------------------
    | Relationship Methods
    |--------------------------------------------------------------------------
    */
    /**
     * many-to-many relationship method.
     *
     * @return QueryBuilder
     */
    public function users()
    {
        return $this->belongsToMany('App'Admin'User');
    }
    /**
     * many-to-many relationship method.
     *
     * @return QueryBuilder
     */
    public function permissions()
    {
        return $this->belongsToMany('App'Admin'Permission');
    }
}

我在这里要做的是创建一个可以创建新角色的页面，并将该角色与已创建的权限相关联：

@foreach ($permissions as $permission)
                            <label class="checkbox">
                                <input type="checkbox" value="{{ $permission->id }}" name="permissions[]" id="permission_{{ $permission }} }}">
                                {{ $permission->permission_title }}
                            </label>
                        @endforeach

在控制器中，我尝试这样做以从页面中提取选定的权限并保存所有内容：

// logic to save role
$role->save();
$permissions = Input::get('permissions');
$role->permissions->sync($permissions);

但是，在执行最后一条语句后，我收到以下错误： exception 'BadMethodCallException' with message 'Method sync does not exist. '我也遇到了同样的错误，attach。另外，我不确定我是否应该在某处提供中间表的名称permission_role？谢谢。