watercat_website/public/plugins/demo/model/PluginDemoModel.php

<?php
// +----------------------------------------------------------------------
// | ThinkCMF [ WE CAN DO IT MORE SIMPLE ]
// +----------------------------------------------------------------------
// | Copyright (c) 2013-2018 http://www.thinkcmf.com All rights reserved.
// +----------------------------------------------------------------------
// | Author: Dean <zxxjjforever@163.com>
// +----------------------------------------------------------------------

namespace plugins\demo\model;

//Demo插件英文名，改成你的插件英文就行了
use think\Model;

//Demo插件英文名，改成你的插件英文就行了,插件数据表最好加个plugin前缀再加表名,这个类就是对应“表前缀+plugin_demo”表
class PluginDemoModel extends Model
{
    //自定义方法
    public function test()
    {
        echo 'hello';
    }
}