The Presenter pattern in Rails

• What are software patterns?
• What is the presenter pattern?
• Why is it used?
• How is it implemented at LP?
• Related patterns.

1 We don't want to re-create the wheel.

2 Patterns are proven solutions.

3 Reduces coupling, increases cohesion.

4 Patterns make communication more efficient.

5 Avoid antipatterns (big ball of mud).

The real reason 4 patterns

MVC (Model–view–controller)

Factory Pattern

Decorator Pattern

MVVM (Presenter Pattern)

Factory Pattern

Factory Pattern

// Types.js - Constructors used behind the scenes
// A constructor for defining new cars
function Car( options ) {
 
  // some defaults
  this.doors = options.doors || 4;
  this.state = options.state || "brand new";
  this.color = options.color || "silver";
 
}
 
// A constructor for defining new trucks
function Truck( options){
 
  this.state = options.state || "used";
  this.wheelSize = options.wheelSize || "large";
  this.color = options.color || "blue";
}
 
 
// FactoryExample.js
// Define a skeleton vehicle factory
function VehicleFactory() {}
 
// Define the prototypes and utilities for this factory
// Our default vehicleClass is Car
VehicleFactory.prototype.vehicleClass = Car;
 
// Our Factory method for creating new Vehicle instances
VehicleFactory.prototype.createVehicle = function ( options ) {
 
  switch(options.vehicleType){
    case "car":
      this.vehicleClass = Car;
      break;
    case "truck":
      this.vehicleClass = Truck;
      break;
    //defaults to VehicleFactory.prototype.vehicleClass (Car)
  }
 
  return new this.vehicleClass( options );
 
};
 
// Create an instance of our factory that makes cars
var carFactory = new VehicleFactory();
var car = carFactory.createVehicle( {
            vehicleType: "car",
            color: "yellow",
            doors: 6 } );
 
// Test to confirm our car was created using the vehicleClass/prototype Car
// Outputs: true
console.log( car instanceof Car );
 
// Outputs: Car object of color "yellow", doors: 6 in a "brand new" state
console.log( car );

Decorator Pattern

Decorator Pattern

var User = function(name) {
    this.name = name;
 
    this.say = function() {
        log.add("User: " + this.name);
    };
}
 
var DecoratedUser = function(user, street, city) {
    this.user = user;
    this.name = user.name;  // ensures interface stays the same
    this.street = street;
    this.city = city;
 
    this.say = function() {
        log.add("Decorated User: " + this.name + ", " +
                   this.street + ", " + this.city);
    };
}
 
// logging helper
 
var log = (function() {
    var log = "";
 
    return {
        add: function(msg) { log += msg + "\n"; },
        show: function() { alert(log); log = ""; }
    }
})();
 
function run() {
 
    var user = new User("Kelly");
    user.say();
 
    var decorated = new DecoratedUser(user, "Broadway", "New York");
    decorated.say();
 
    log.show();
}

=   MVC

Mr. Waldorf chooses

Rails MVC + Presenter

Presenter Design Pattern

Presenter benefits

• Testable view layer
• Package data as the view likes it (formatting , aggregate model data)
• Validate data + consolidate errors
• Lean Views and Controllers
• rails_helper.rb vs presenter?

Let's look at CODE

https://github.com/lonelyplanet/hotels

Resources

• http://robertomurray.co.uk/blog/2014/decorators-presenters-delegators-rails/
• http://blog.jayfields.com/2007/03/rails-presenter-pattern.html
• http://programmers.stackexchange.com/questions/141843/what-is-the-actual-purpose-of-mvc
• http://blog.jayfields.com/2006/09/rails-model-view-controller-presenter.html
• http://betterexplained.com/articles/intermediate-rails-understanding-models-views-and-controllers
• http://rvlasveld.github.io/blog/2013/09/26/rails-presenters-filling-the-model-view-controller-gap/
• http://nithinbekal.com/posts/rails-presenters