Node.js 错误引用错误：未在使用mongodb的NodeJ中定义db

我正在尝试使用post方法，并在注册过程中保存有关用户的信息，但我遇到了这个错误，有人知道如何解决吗？ 我试图在网上搜索，但一切都对我有用。 我的文件组织是否正确？或者我应该创建另一个名为database.js的文件？在www.js中，我插入了到服务器的连接和到数据库的连接，但我不知道是否正确。 感谢所有能帮助你的人

我的app.js文件

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');


//DB
//var mongo = require('mongodb');

//var server = require('./routes/server');
var index = require('./routes/index');
var Registration = require('./routes/Registration');
var login = require('./routes/login');
var app = express();
//var db = require('./config/challengeskill');

// view engine setup

app.set('views', path.join(__dirname, 'views'));

app.set('view engine', 'ejs');


// uncomment after placing your favicon in /public

//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));



app.use('/', index);
app.use('/Registration',Registration);
app.use('/login',login);


app.post('/registrationform', (req, res) => {

db.collection('user').save(req.body, (err,result)=>{
  if(err) return console.log(err)

  console.log('saved to database')
  res.redirect('/')
})
});

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;

我的www.js文件 #!/usr/bin/env节点

/**
 * Module dependencies.
 */

    var app = require('../app');
var debug = require('debug')('challengeskill:server');
var http = require('http');
var MongoClient = require('mongodb').MongoClient;
var db;
var url = 'mongodb://localhost:27017/user';

/**
 * Get port from environment and store in Express.
 */

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);


/**
 * Gconnect DB.
 */

MongoClient.connect(url, function (err, database) {
    if (err) {
    throw err;
    }
    else {
  ///////////////////////////
    database = db;
    console.log("connected to DB");

}
});

/**
 * Create HTTP server.
 */

var server = http.createServer(app);

/**
 * Listen on provided port, on all network interfaces.
 */

server.listen(port);
server.on('error', onError);
server.on('listening', onListening);

/**
 * Normalize a port into a number, string, or false.
 */

function normalizePort(val) {
  var port = parseInt(val, 10);

  if (isNaN(port)) {
    // named pipe
    return val;
  }

  if (port >= 0) {
    // port number
    return port;
  }

  return false;
}

/**
 * Event listener for HTTP server "error" event.
 */

function onError(error) {
  if (error.syscall !== 'listen') {
    throw error;
  }

  var bind = typeof port === 'string'
    ? 'Pipe ' + port
    : 'Port ' + port;

  // handle specific listen errors with friendly messages
  switch (error.code) {
    case 'EACCES':
  console.error(bind + ' requires elevated privileges');
  process.exit(1);
  break;
    case 'EADDRINUSE':
  console.error(bind + ' is already in use');
  process.exit(1);
  break;
default:
  throw error;
  }
}

/**
 * Event listener for HTTP server "listening" event.
 */

function onListening() {
  var addr = server.address();
  var bind = typeof addr === 'string'
    ? 'pipe ' + addr
    : 'port ' + addr.port;
  debug('Listening on ' + bind);
}

这是我的文件，已经整理好了

>ChallengeSkill
>>.idea
>>bin
---->www
>>node_modules
>>public
>>routes
---->index.js
---->login.js
---->Registration.js
---->users.js
>>views
---->error.ejs
---->index.ejs
---->login.ejs
---->Registration.ejs
app.js
ChallengeSkill.iml
package.json

---

在您的www.js文件中，您可能希望交换该行

database = db;

像这样：

db = database;

---

您的代码很好，但是您正在将返回的

数据库

值赋给一个名为

db

的空变量，因此只需交换这些值，就可以按预期工作