I am getting the error User.create not a function.

var express = require('express');
var router = express.Router();
var User = require('../models/user');

//GET /register
router.get('/register', function(req, res, next) {
  return res.render('register', { title: 'Sign Up' });
});

//POST /register
router.post('/register', function(req, res, next) {
  if (
    req.body.email &&
    req.body.name &&
    req.body.favoriteBook &&
    req.body.password &&
    req.body.confirmPassword
  ) {
    if (req.body.password != req.body.confirmPassword) {
      var err = new Error('Passwords do not match');
      err.status = 400;
      return next(err);
    }

    var userData = {
      email: req.body.email,
      name: req.body.name,
      favoriteBook: req.body.favoriteBook,
      password: req.body.password
    };
    //use schema's 'create' method to insert document into Mongo
    User.create(userData, function(error, user) {
      if (error) {
        return next(error);
      } else {
        return res.redirect('/profile');
      }
    });
  } else {
    var err = new Error('All fields required.');
    err.status = 400;
    return next(err);
  }
});
// GET /
router.get('/', function(req, res, next) {
  return res.render('index', { title: 'Home' });
});

// GET /about
router.get('/about', function(req, res, next) {
  return res.render('about', { title: 'About' });
});

// GET /contact
router.get('/contact', function(req, res, next) {
  return res.render('contact', { title: 'Contact' });
});

module.exports = router;

var express = require('express');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var app = express();

//mongodb connection
mongoose.connect('mongodb://localhost:27017/bookworm');
var db = mongoose.connection;

//mongo error
db.on('error', console.error.bind(console, 'connection error'));
// parse incoming requests
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));

// serve static files from /public
app.use(express.static(__dirname + '/public'));

// view engine setup
app.set('view engine', 'pug');
app.set('views', __dirname + '/views');

// include routes
var routes = require('./routes/index');
app.use('/', routes);

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

// error handler
// define as the last app.use callback
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});

// listen on port 3000
app.listen(3000, function() {
  console.log('Express app listening on port 3000');
});