mongoose and node error : Cannot call method 'model' of undefined - node.js

Question

I tried following a tutorial on mongoose/mongodb with node and have fallen into issues trying to get express/node to res.send json documents from the collection.
The following code is producing errors when I try to access localhost:3000/mongodb
The database and collection exist. The collection has 3 documents.
app.js
/**
* Module dependencies.
*/
var express = require('express');
var http = require('http');
var path = require('path');
var mongoose = require('mongoose');
var app = module.exports = express();
// all environments
app.set('port', process.env.PORT || 3000);
app.set('views', __dirname + '/views');
app.engine('html', require('hogan-express'));
app.use(express.favicon());
app.use(express.logger('dev'));
app.use(express.bodyParser());
app.use(express.methodOverride());
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));
mongoose.connect('mongodb://localhost/xkayak');
var schema = new mongoose.Schema({ username: 'string', email: 'string', password: 'string'});
var usercollection = mongoose.model('usercollection', schema);
// development only
if ('development' == app.get('env')) {
app.use(express.errorHandler());
}
require('./routes/index.js');
http.createServer(app).listen(app.get('port'), function(){
console.log('Express server listening on port ' + app.get('port'));
});
index.js --the routes file
var app = require('../app.js');
app.get('/mongodb', function(req, res) {
app.mongoose.model('usercollection').find(function(err, usercollection) {
res.send(usercollection);
});
});
The error produced is:
500 TypeError: Cannot call method 'model' of undefined
What is wrong with my code? Did I set up the collection incorrectly? If I remove this code everything else works.

Answer 1

In your route, you are importing app. The problem is here:
var app = module.exports = express();
This means that when you import app.js you're going to get an instance of express, and not mongoose like you think when you do app.mongoose.model....
Consider:
app.js:
var app = express();
exports.express = app;
...
var mongoose = mongo.connect(...);
exports.mongoose = mongoose;
index.js:
app.express.get( ...
app.mongoose.model(...);
);