node.js - mongodb cryptic error process.nextTick(function() { throw err; }) ^ Error at Object.<anonymous> -

when attempting start mean app after adding mongoose , couple of mongoose schemas, i'm getting strange error.

node_modules/mongoose/node_modules/mongodb/lib/server.js:228         process.nexttick(function() { throw err; })                                             ^ error     @ object.<anonymous> (/projects/node/flapper-news/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/error.js:42:24)     @ module._compile (module.js:460:26)     @ object.module._extensions..js (module.js:478:10)     @ module.load (module.js:355:32)     @ function.module._load (module.js:310:12)     @ module.require (module.js:365:17)     @ require (module.js:384:17)     @ object.<anonymous> (/projects/node/flapper-news/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/index.js:2:17)     @ module._compile (module.js:460:26)     @ object.module._extensions..js (module.js:478:10) 

app.js

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'); var mongoose = require('mongoose');  require('./models/posts'); require('./models/comments'); mongoose.connect('mongodb://localhost/news');  var routes = require('./routes/index'); var users = require('./routes/users');  var app = express();  // view engine setup app.set('views', path.join(__dirname, 'views')); app.set('view engine', 'ejs');  // uncomment after placing favicon in /public //app.use(favicon(__dirname + '/public/favicon.ico')); app.use(logger('dev')); app.use(bodyparser.json()); app.use(bodyparser.urlencoded({ extended: false })); app.use(cookieparser()); app.use(express.static(path.join(__dirname, 'public')));  app.use('/', routes); app.use('/users', users);  // catch 404 , forward error handler app.use(function(req, res, next) {   var err = new error('not found');   err.status = 404;   next(err); });  // error handlers  // development error handler // print stacktrace if (app.get('env') === 'development') {   app.use(function(err, req, res, next) {     res.status(err.status || 500);     res.render('error', {       message: err.message,       error: err     });   }); }  // production error handler // no stacktraces leaked user app.use(function(err, req, res, next) {   res.status(err.status || 500);   res.render('error', {     message: err.message,     error: {}   }); });   module.exports = app; 

routes

var express = require('express'),     router = express.router(),     mongoose = require('mongoose'),     post = mongoose.model('post'),     comment= mongoose.model('comment');  /* home page. */ router.get('/', function(req, res, next) {     res.render('index', { title: 'express' }); });  router.get('/posts', function(req, res, next) {     post.find(function(err, posts){         if(err){             return next(err);         }          res.json(posts);     }); });  router.post('/posts', function(req, res, next) {     var post = new post(req.body);      post.save(function(err, post) {         if (err) {             return next(err);         }         res.json(post);     }); });  module.exports = router; 

schemas

var mongoose = require('mongoose');  var postschema = new mongoose.schema({     title: string,     link: string,     upvotes: {type: number, default: 0},     comments: [{ type: mongoose.schema.types.objectid, ref: 'comment' }] });  mongoose.model('post', postschema);  var commentschema = new mongoose.schema({     body: string,     author: string,     upvotes: {type: number, default: 0},     post: { type: mongoose.schema.types.objectid, ref: 'post' } });  mongoose.model('comment', commentschema); 

i had schemas , mongoose connect call after declaring app = express() in app.js, threw different error. can spot i've gone wrong?

i hadn't created /data/db directory mongodb install. created directory , set myself owner, , works now.