node_mysql.js

require('dotenv').config();
var mysql = require('mysql');
let hosPool = mysql.createPool({
  host: process.env.HOS_HOST,
  user: process.env.HOS_USER,
  password: process.env.HOS_PASSWORD,
  database: process.env.HOS_DATABASE,
  port: process.env.HOS_PORT
});

hosPool.on('connection', (connection) => {
  connection.query('SET NAMES utf8')
});

app.use((req, res, next) => {
  req.hosPool = hosPool;
  next();
});

//============== in model =======//
getHPID(pool, cid) {
    let q = Q.defer();
    pool.getConnection((err, conn) => {
      if (err) {
        console.log(err)
        q.reject(err)
      } else {
        let sql = `select concat(HOSPCODE, PID) as hpid
          from person 
          where cid=?`;
        conn.query(sql, [cid], function (err, rows) {
          if (err) q.reject(err);
          else q.resolve(rows)
        });

        conn.release()
      }
    });

    return q.promise;
  }