apisongcan/application/index/validate/RoleValidate.php

<?php

namespace app\index\validate;

use think\Validate;

class RoleValidate extends Validate
{
    protected $rule = array(
        'role_name'   => 'require|unique:role',
    );
    protected $message = array(
        'role_name.require'    => '角色已经存在',
    );
}