Cannot return values to response with mongoose/mongodb and nodejs

Question

I am using Nodejs, ExpressJs, MongoDB via Mongoose. I have created a simple UserSchema . I have my code separated into multiple files because I foresee them getting complex.

The url '/api/users' is configured to call the list function in 'routes/user.js' which happens as expected. The list function of UserSchema does get called, but it fails to return anything to the calling function and hence no result goes out.

What am I doing wrong ?

I tried to model it based on http://pixelhandler.com/blog/2012/02/09/develop-a-restful-api-using-node-js-with-express-and-mongoose/

I think I am doing something wrong with the function definition of userSchema.statics.list

app.js

users_module = require('./custom_modules/users.js'); // I have separated the actual DB code into another file
mongoose.connect('mongodb:// ******************');

var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function callback() {
    users_module.init_users();
});

app.get('/api/users', user.list);

custom_modules/users.js

function init_users() {
    userSchema = mongoose.Schema({
        usernamename: String,
        hash: String,
    });

    userSchema.statics.list = function () {
        this.find(function (err, users) {
            if (!err) {
                console.log("Got some data"); // this gets printed 

                return users; // the result remains the same if I replace this with return "hello" 
            } else {
                return console.log(err);
            }
        });
    }

    UserModel = mongoose.model('User', userSchema);
} // end of init_users

exports.init_users = init_users;

routes/user.js

exports.list = function (req, res) {
    UserModel.list(function (users) {
        // this code never gets executed
        console.log("Yay ");

        return res.json(users);
    });
}

Is it giving any error?

Amol M Kulkarni
– Amol M Kulkarni

2013-08-21 06:56:50 +00:00
Commented Aug 21, 2013 at 6:56 — Amol M Kulkarni
– Amol M Kulkarni, Commented Aug 21, 2013 at 6:56

Amol M Kulkarni · Accepted Answer · 2013-08-21 07:26:18Z

1

Actually in your code you are passing a callback, which is never handled in function userSchema.statics.list

You can try the following code:

userSchema.statics.list = function (calbck) {    
  this.find(function (err, users) {
    if (!err) {        
      calbck(null, users); // this is firing the call back and first parameter should be always error object (according to guidelines). Here no error, so pass null (we can't skip)
    } else {    
         return calbck(err, null); //here no result. But error object. (Here second parameter is optional if skipped by default it will be undefined in callback function)
      }
    });    
 }

Accordingly, you should change the callback which is passed to this function. i.e.

exports.list = function (req, res){
UserModel.list(function(err, users) {
   if(err) {return console.log(err);}
   return res.json(users);
  });
}

edited Aug 21, 2013 at 7:26

answered Aug 21, 2013 at 6:58

Amol M Kulkarni

21.7k34 gold badges125 silver badges165 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

geeky_monster Over a year ago

Yeah . Will do . Testing it out a bit.

geeky_monster Over a year ago

I learn quite a bit of new things today. I always assumed callbacks get called by themselves . Till now I used functions that had callbacks already defined into their definitions. So I just made use of them and assumed that every function can have a callback and that the callback gets executed automatically after the function is complete .

Collectives™ on Stack Overflow

Cannot return values to response with mongoose/mongodb and nodejs

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related