Node.js：无法调用未定义的方法版本（MySql）

Question

So great part of this is that this same code works on my development machine.

I'm trying to deploy it to the production server, and i'm getting this error: Cannot call method release of undefined. This works on my box, so why is that not working in production is what confuses me. I downloaded the code with all the modules, then tried to do npm install, and still manually deploy express and mysql, but no luck.

The infringing line is: connection.release();

If i rem that line, then it will just hang on anything trying to call connection.

The code:

process.env.TZ = 'UTC';
var express    = require("express");
var mysql      = require('mysql');

var pool      =    mysql.createPool({
    connectionLimit : 100, //important
    host     : 'localhost',
    user     : 'thedbuser',
    password : 'thedbpass',
    database : 'thedatabase',
    debug    :  false,
    timezone: 'utc'
});

var app = express();

function get_data(req,res) {

    pool.getConnection(function(err,connection){
        if (err) {
          connection.release();
          res.json({"code" : 100, "status" : "Error in connection database"});
          return;
        }   

        console.log('connected as id ' + connection.threadId);
        var id = Number(req.param("id"));

        connection.query("select * from thetable WHERE id = ?" , [id], function(err,rows){
            connection.release();
            if(!err) {
                res.json(rows);
            }           
        });

        connection.on('error', function(err) {      
              res.json({"code" : 100, "status" : "Error in connection database"});
              return;     
        });
  });
}

app.get("/id",function(req,res){

  get_data(req,res);

});

app.listen(3000);

Answer 1

pool.getConnection(function(err,connection){
    if (err) {
      connection.release();
      res.json({"code" : 100, "status" : "Error in connection database"});
      return;
    }   

So inside the if (err) block means there was an error. The node.js generic callback API semantic is when an err is passed to the callback function, the success/result variable is not guaranteed to also be provided. In this case, since there was an error getting a connection, no connection object is passed to the callback - because the error prevented the connection from happening correctly. Thus you can probably safely just delete the connection.release() line but if you know there is a case where both err and connection will both be passed (I suspect there is no such case), you could guard your call to connection.release() with an if (connection) block or a logical operator like connection && connection.release()