_working-using-domains.md

Working using domains

In this example we'd like to have a factory that works per request and allows to keep track of created Models We create a factory per request and create a domain to which we attach the factory That way the singleton is automatically shared with all parts of the application under process.domain.*

app.js

var express = require('express'),
    domain = require('domain'),
    factory = require('./factory'),
    View = require('./view'),
    app = express();

app.all('*', function(req, res, next) {
    // We create a factory for every request and attach it to a new domain
    // That way it is automatically available in all code executed in the context of this request
    
    var requestDomain = domain.create();
    var perRequestFactory = factory();

    requestDomain.factory = perRequestFactory;

    requestDomain.run(function () {
        var view = new View({
            collapsed: req.cookie.viewState.collapsed,
            hidden: req.cookie.viewState.hidden
        });

        var responseTime = Math.random() * 2500; // random response time
        // Simulate async tasks
        setTimeout(function () {
            res.send(perRequestFactory.serializeModels());
        }, responseTime);
    });

});

app.listen(8000);

factory.js

// Basically a factory for factories
// For every request we create a new one

var Model = require('backbone').Model;

module.exports = function createFactory () {
    var allModels = [];

    return {
        createModel: function (data) {
            var model = new Model(data);
            allModels.push(model);
            return model;
        },
        serializeModels: function () {
            return allModels.map(function (model) {
                return model.toJSON();
            });
        },
        reset: function () {
            allModels = [];
        }
    }
};

view.js

var View = require('backbone').View;

module.exports = View.extend({
    initialize: function (options) {
        this.viewState = process.domain.factory.createModel({
            collapsed: options.collapsed,
            hidden: options.hidden
        });
    }
});