Passing reference to DB into routes is not working for my Node / Express project

Question

I am using node + express to create a simple REST API, and am trying to separate out routing logic from db logic. I am having a problem getting access to the DB from the routes.

Here is my server.js code:

var express = require('express')
  , path = require('path')
  , http = require('http')
  , mongo = require('mongodb');

// Configure Express app
var app = express();
app.configure(function () {
    app.set('port', process.env.PORT || 3000);
    app.use(express.logger('dev'));  /* 'default', 'short', 'tiny', 'dev' */
    app.use(express.bodyParser()),
    app.use(express.static(path.join(__dirname, 'public')));
});

// Configure DB
var Server = mongo.Server
  , Db = mongo.Db
  , BSON = mongo.BSONPure
  , server = new Server('localhost', 27017, {auto_reconnect: true})
  , db = new Db('mydb', server, {safe: true});

// Open DB to see if we need to populate with data
db.open(function(err, db) {
  if(!err) {
    console.log("Connected to 'mydb' database");
    var Post = require('./routes/posts')
      , post = new Post(db);

    // Set the routes
    app.get('/:org/posts', post.find);
    app.get('/:org/posts/:id', post.get);
    app.post('/:org/posts', post.add);
    app.put('/:org/posts/:id', post.update);
    app.delete('/:org/posts/:id', post.remove);

    // Fire up the server
    http.createServer(app).listen(app.get('port'), function () {
      console.log("Express server listening on port " + app.get('port'));
    });
  }
});

and here is the logic in the post.js file:

var Post = function(db) {
  this.db = db;
};

Post.prototype.get = function(req, res) {
  var id = req.params.id;
  var org = req.params.org;
  var db = this.db;

  console.log('Retrieving post: ' + id + ' from org: ' + org);
  db.collection('ads', function(err, collection) {
    collection.findOne({'_id':new BSON.ObjectID(id), 'org':org}, function(err, item) {
      res.send(item);
    });
  });
};

Post.prototype.find = function(req, res) {
  var org = req.params.org;
  var db = this.db;

  console.log('Finding posts for org: ' + org);
  db.collection('posts', function(err, collection) {
    collection.find({'org':org}).toArray(function(err, items) {
      res.send(items);
    });
  });
};

Post.prototype.add = function(req, res) {
  var org = req.params.org;
  var post = req.body;
  var db = this.db;

  console.log('Adding post: ' + JSON.stringify(post) + ' for org: ' + org);
  db.collection('posts', function(err, collection) {
    collection.insert(post, {safe:true}, function(err, result) {
      if (err) {
        res.send({'error':'An error has occurred'});
      } else {
        console.log('Success: ' + JSON.stringify(result[0]));
        res.send(result[0]);
      }
    });
  });
};

Post.prototype.update = function(req, res) {
  var id = req.params.id;
  var org = req.params.org;
  var post = req.body;
  var db = this.db;

  delete post._id;
  console.log('Updating post: ' + id + ', org: ' + org);
  console.log(JSON.stringify(post));
  db.collection('posts', function(err, collection) {
    collection.update({'_id':new BSON.ObjectID(id)}, post, {safe:true}, function(err, result) {
      if (err) {
        console.log('Error updating post: ' + err);
        res.send({'error':'An error has occurred'});
      } else {
        console.log('' + result + ' document(s) updated');
        res.send(post);
      }
    });
  });
};

Post.prototype.remove = function(req, res) {
  var id = req.params.id;
  var org = req.params.org;
  var db = this.db;

  console.log('Deleting post: ' + id + ', org: ' + org);
  db.collection('posts', function(err, collection) {
    collection.remove({'_id':new BSON.ObjectID(id), 'org':org}, {safe:true}, function(err, result) {
      if (err) {
        res.send({'error':'An error has occurred - ' + err});
      } else {
        console.log('' + result + ' document(s) deleted');
        res.send(req.body);
      }
    });
  });
};

module.exports = Post;

I would think that the post object would hold on to the db reference for use when it is called from the routes, but I get the following error:

TypeError: Cannot call method 'collection' of undefined
    at Post.find (../routes/posts.js:23:6)

Can anyone point me in the right direction? Many thanks

score 7 · Answer 1 · answered May 10 '14 at 17:34

Try this way. It became my favourite way of writing modules since I found this on Stack Overflow some time ago.

server.js:

...    
var Post = require('./routes/posts')(db);
...

posts.js:

...
module.exports =function(db) {
        var module = {};

         module.get = function(req, res){
            ...
            /* db should be accessible here */

         }

         return module;
}

score 1 · Accepted Answer · answered Jan 04 '13 at 00:58

1

Your post object is lost as the this in your Post methods when called by the Express route handlers you're registering. You need to bind the methods to your post instance so that no matter how they're called by Express, this will be your post. Like this:

// Set the routes
app.get('/:org/posts', post.find.bind(post));
app.get('/:org/posts/:id', post.get.bind(post));
app.post('/:org/posts', post.add.bind(post));
app.put('/:org/posts/:id', post.update.bind(post));
app.delete('/:org/posts/:id', post.remove.bind(post));

answered Jan 04 '13 at 00:58

JohnnyHK

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This works - thanks. It does not seem that this is the standard way to pass a DB reference into controller objects (will this still be non-blocking?). Do you have advice on how to make this simpler? I want to get this right before I add tons more routes. Many thanks for helping out on this! – Scott Switzer Jan 04 '13 at 12:50
Use the `Post` module as a singleton rather than having it export a class you instantiate in `server.js`. Using [Mongoose](http://mongoosejs.com/) instead of directly using the native driver also helps because of its default database connection concept. – JohnnyHK Jan 04 '13 at 13:40

Passing reference to DB into routes is not working for my Node / Express project

2 Answers2