问如何在laravel 5.3中检查模型实例是否附加到相关的模型实例？

EN

class RolePermissionController extends Controller
{
    // POST /roles/1/permissions/2/sync
    // BODY {isAllowed: true} 
    // $role - instance of role model with id == 1
    // $permission - instance of permission model with id == 2
    // roles and permissions has many to many relationship
    public function synchronize(Request $request, Role $role, Permission $permission)
    {
        $this->authorize($permission);

        $this->validate($request, [
            'isAllowed' => 'required|boolean'
        ]);

        // I want to check here if the permission is attached to the role

        if ($request->input('isAllowed')) {
            $role->perms()->attach($permission);
        } else {
            $role->perms()->detach($permission);
        }

    }
}