node.js - 我想把mysql promise async化，为什么出现错误？

以下代码是运行不了的：

/**
 * Created by lqq on 2016/11/16.
 */
 "use strict";
 var Promise=require('bluebird');
 var mysql=Promise.promisifyAll(require('mysql'));
 var pool=mysql.createPool({
     host:'192.168.0.186',
     port:5000,
     user:'root',
     password:'',
     database:'ele'
 });

 var orm=module.exports={};

 orm.createConn = async function () {
     let conn= await pool.getConnectionAsync();
     return Promise.promisifyAll(conn);
 };

 orm.query= async function(name,obj){
     let conn=orm.createConn();
     let res= await conn.createQueryAsync('select * from caseinfo',{});
     pool.releaseConnection(conn);
     return res;
 };

请问是为什么？