Converting Mongoose model functions to be Promise and callback friendly simultaneously

I just started using promises in one of my Node.js applications after watching the callback hell in some of the code there.

I was going to use Q but while checking the different options I stumbled upon Bluebird and I liked it.

At some time I checked how Mongoose works with promises and discovered that many functions return a promise and also the queries’ exec() returns a promise too. The Promise in Mongoose is mpromise.

However I decided to stick to a single implementation of Promise for my entire application to have something as a standard and predictable way to use “promisified” functions. And this happened to be Bluebird. It’s huge(features) and I like it!

The first thing to “clean” was a function in one of my Mongoose’s models: User.create() – a custom static function that overrides the default create function. I needed the override to be able to receive custom structured arguments and also to do some changes before the model data is saved. I changed the way I handle the create later by removing it and using pre-hooks instead but this is a good example to show and is like a repeatable template for any other function that is going to be converted the same way.

Let’s see the original Promise-free function:

userSchema.static('create', function (data, cb) {
  var user = new User({
    facebookId: data.facebookId,
    accessToken: hat(),
    name: data.name,
    photo: data.photo
  });
  return user.save(cb);
});

You can see that User.create() receives a data object literal and executes the callback cb after it’s saved.

An example usage of create will be:

User.create({
  facebookId: '68yc7j9y4f64',
  name: 'Iliyan Trifonov',
  photo:'https://...'
}, function userCreateCb (err, user) {
  if (err) {
    return console.error(err);
  }
  if (!user) {
   return console.error('User not created!');
  }
  console.info('User created successfully!', user);
});

Now let’s make User.create return a promise:

First we promisify the model with:

Promise.promisifyAll(User);
Promise.promisifyAll(User.prototype);

and then the create function will look like:

userSchema.static('create', function (data) {
  var user = new User({
    facebookId: data.facebookId,
    accessToken: hat(),
    name: data.name,
    photo: data.photo
 });
 return user.saveAsync();
});

Now we should handle the resolve and reject:

User.create({
  facebookId: '68yc7j9y4f64',
  name: 'Iliyan Trifonov',
  photo:'https://...'
}).then(function (user) {
  console.info('User created successfully!', user);
}).catch(function (err) {
  console.error('Error creating the user!', err);
});

For now I am experimenting with the then(resolveCb)/catch(errorCb) combination but it can be changed to then(resolveCb, rejectCb) or then(resolveCb)/then(null, rejectCb).

But what about the rest of the code that depends on User.create to use a callback?

Let’s add the callback argument again:

userSchema.static('create', function (data, cb) {
  var user = new User({
    facebookId: data.facebookId,
    accessToken: hat(),
    name: data.name,
    photo: data.photo
  });
  return user.saveAsync().then(function (user) {
    return cb(null, user);
  }).catch(function (err) {
    return cb(err);
  });
});

And now the create function will work with the legacy code and the new Promises code simultaneously!

 

Install x265 codec on Ubuntu 14.04

x265 is here and we have to deal with its support.

So using these commands I was able to play a x265 encoded video in the latest Ubuntu:

sudo apt-add-repository ppa:strukturag/libde265
sudo apt-get update
sudo apt-get install gstreamer1.0-libde265

Source: Install x265 codec on Ubuntu 14.04