Coalesce.js is a robust and stable framework for syncing client state with a persistent backend such as a REST API or socket connection. Defining characteristics of coalesce include:

• Correctness is paramount. All other features, including performance, are important, but secondary.
• Built around synchronization. Models are never locked and framework semantics assume updates are always coming in from a backend.
• Full support for relationships. Related models can be saved concurrently and the framework will automatically order requests around foreign key dependencies.
• Robust handling of conflicts and errors.
• Forking models is first-class within the framework.
• All operations are structured around javascript promises.

Coalesce is a functional alternative to ember-data and is used in production at Outreach with dozens of inter-related models.

For now, as coalesce is in development, follow the development instructions to use coalesce. The build-browser command will create browser-compatible distributables in the dist folder. Include coalesce.js in the page after ember.js.

By default, coalesce assumes that the backend is a REST api which sticks to pretty much the same conventions as ember-data's RESTAdapter needs. There are a few differences however:

• EPF sets a client_id in the JSON for every model and expects this to be echoed back by the server. It uses this to keep it's internal idmap up to date.
• Related keys still need to use _id and _ids (this is different from ember-data 1.0 beta 2)

All models within coalesce are subclasses of Ep.Model. For example:

App.Post = Ep.Model.extend({
  title: Ep.attr('string'),
  body: Ep.attr('string'),

  comments: Ep.hasMany(App.Comment),
  user: Ep.belongsTo(App.User)
});

The primary means of interacting with coalesce is through a session. Coalesce automatically injects a primary session into all routes and controllers. To load data, you can use the load method on the session:

App.PostRoute = Ember.Route.extend({

  model: function(params) {
    return this.session.load('post', params.post_id);
  }

});

For compatibility with the behavior of the Ember.js router, a find method is also placed on models. The above code is equivalent to:

App.PostRoute = Ember.Route.extend({

  model: function(params) {
    return App.Post.find(params.post_id);
  }

});

The find method is the only method that is available on the models themselves and it is recommended to go through the session directly.

By default, Ember.js will automatically call the find method, so the above route can actually be simplified to:

App.PostRoute = Ember.Route.extend({
  // no model method required, Ember.js will automatically call `find` on `App.Post`
});

The session object also has other methods for finding data such as query.

To mutate models, simply modify their properties:

post.title = 'updated title';

To persist changes to the backend, simply call the flush method on the session object.

post.title = 'updated title';
session.flush();

In coalesce, most things are promises. In the above example you could listen for when the flush has completed using the promise API:

post.title = 'updated title';
session.flush().then(function(models) {
  // this will be reached if the flush is successful
}, function(models) {
  // this will be reached only if there are errors
});

Sessions can be flushed at any point (even if other flushes are pending) and re-trying errors is as simple as performing another flush:

post.title = 'updated title';
session.flush().then(null, function() {
  // the reject promise callback will be invoked on error
});

// do something here that should correct the error (e.g. fix validations)

session.flush(); // flush again

Models also have an errors property which will be populated when the backend returns errors.

Changes can be isolated easily using child sessions:

var post = session.load(App.Post, 1);

var childSession = session.newSession(); // this creates a "child" session

var childPost = childSession.load(App.Post, 1); // this record instance is separate from its corresponding instance in the parent session

post === childPost; // returns false, they are separate instances
post.isEqual(childPost); // this will return true

childPost.title = 'something'; // this will not affect `post`

childSession.flush(); // this will flush changes both to the backend and the parent session, at this point `post` will have its title updated to reflect `childPost`

To build coalesce, follow the instructions below:

• Install node.
• git clone https://github.com/coalescejs/coalesce
• cd coalesce
• npm install
• npm test to run the tests via mocha
• To build a browser distributable, run the build-browser command in the repository root with ember-script build-browser (make sure to install ember-script globally).

You can join the email discussion group to get help, as well as discuss new features and directions for Coalesce. Please post any questions, interesting things you discover or links to useful sites for Coalesce users.