node-mysql: connect时的”Cannot enqueue Handshake after already enqueuing a Hand shake”错误

events.js:160
      throw er; // Unhandled 'error' event
      ^


Error: Cannot enqueue Handshake after invoking quit.
    at Protocol._validateEnqueue (D:\bookstore\node_modules\mysql\lib\protocol\Protocol.js:202:16)
    at Protocol._enqueue (D:\bookstore\node_modules\mysql\lib\protocol\Protocol.js:135:13)
    at Protocol.handshake (D:\bookstore\node_modules\mysql\lib\protocol\Protocol.js:52:41)
    at Connection.connect (D:\bookstore\node_modules\mysql\lib\Connection.js:130:18)
    at D:\bookstore\build\dev-server.js:50:14
    at Layer.handle [as handle_request] (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\layer.js:95:5)
    at next (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\route.js:137:13)
    at Route.dispatch (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\layer.js:95:5)
    at D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:281:22
    at param (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:354:14)
    at param (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:365:14)
    at Function.process_params (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:410:3)
    at next (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:275:10)
    at Function.handle (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:174:3)
    at router (D:\bookstore\node_modules\_express@4.15.3@express\lib\router\index.js:47:12)

原文地址 https://www.mgenware.com/blog/?p=2924&utm_source=tuicool&utm_medium=referral

本文测试环境: Node.js 4.2.2, node-mysql 2.9.0

使用node-mysql遇到Cannot enqueue Handshake after already enqueuing a Hand shake。这个错误提示意思是某个数据库链接已经执行了，不能进行屡次链接了。遇到此类状况，首先看下代码是否出现了同一个数据库链接屡次调用connect方法的状况，这种明显的错误排除后，看看是否在调用connect前发生了隐式的链接操做，好比在未链接时直接调用query作查询会间接去connect，以下代码，createConnection后直接调用query也会触发链接：

var mysql = require('mysql');
mysql.createConnection({...}).query('...', (err, res) => {
    if (err) {
        // 处理错误
    }
    // 隐式链接，没有链接错误的话，数据会正常返回
});

固然，也能够直接去掉显式的connect调用，任由query去作隐式链接，也不会出现上述错误，不过若是这样的话，强烈建议使用Pool，这样数据库链接能够最大化的实现复用和管理，和createConnection返回的链接同样，Pool能够经过getConnection返回一个链接，也能够直接用query去自动复用或建立一个链接。不过若是使用pool.getConnection的话，记得用完链接后调用connection.release把链接返回给Pool。这两种方式多数状况下是等价的，除非查询包含多个语句，能够参考这个连接：Difference between using getConnection() and using pool directly in node.js with node-mysql module?.