Review: Models

• Application data is stored in a database
• Working with databases is hard, so we use Models to simplify the work
• ActiveRecord provides us with methods to easily work with the database
• We can use rails console as an enhanced IRB environment that includes our Rails app classes

IN views/tweets/index.html.erb

Where does @tweets come from?

• We know it is an array of Tweet instances
• We know Tweet instance responds to methods for its attributes (e.g. .body and .handle)
• We still don't know how @tweets gets initialized...

Controllers

• Controllers talk to the database, and pass data to the views
• They use Models to talk to the database
• They use instance variables to pass data to the views
• Controllers are custom Ruby classes that inherit from ApplicationController, just like how Models are custom classes that inherit from ActiveRecord::Base

Controller for each Resource

• The same way we have a Model for each resource, we have a Controller for each resource
• For the tweets resource, we have a Tweet model class, and a TweetsController controller class
• For the users resource, we have a User model class, and a UsersController controller class
• Note the plurality on models (singular) and controllers (plural)

How does it all fit together?

URL -> Controller -> Method

• When you visit /tweets, it instantiates the TweetsController class and calls the index method on it
• When you visit /tweets/new, it instantiates the TweetsController and calls the new method on it
• When you visit /users/1/edit, it instantiates the UsersController and calls the edit method on it

Actions

Inside a Controller class, the methods (e.g. index and new) are referred to as actions.

Code-Along

Let's take a look at the code inside app/controllers to get a better sense of what Controller code looks like.

The Map

Routes

• These mappings of a particular URL pattern onto a particular Controller and Action are known as routes
• Routes are how users access your applications (think of them as gateways into your database)
• Eventually, these mappings will become second nature
• In the meantime, you can use a command in your terminal to see all the routes:

$ rake routes

rake routes

$ rake routes
    Prefix Verb   URI Pattern                Controller#Action
    tweets GET    /tweets(.:format)          tweets#index
           POST   /tweets(.:format)          tweets#create
 new_tweet GET    /tweets/new(.:format)      tweets#new
edit_tweet GET    /tweets/:id/edit(.:format) tweets#edit
     tweet GET    /tweets/:id(.:format)      tweets#show
           PATCH  /tweets/:id(.:format)      tweets#update
           PUT    /tweets/:id(.:format)      tweets#update
           DELETE /tweets/:id(.:format)      tweets#destroy

Q. So, where did all these 'routes' come from?

A. Rails Scaffolding created them for you, in the routes.rb file. A set of routes were created for each resource.

routes.rb

Rails.application.routes.draw do

  resources :tweets

  resources :users

end

routes.rb

• In the routes.rb file, the resources method allows you to create a collection of routes in one line
• Just by typing resources :tweets, Rails will create all of the routes associated with the tweets resource (e.g. everything we saw in the rake routes output)
• The resources method is the simplest way to create a set of CRUD routes for a given resource
• When you scaffold a resource, it places the resources declaration for the resource in the routes.rb file automatically

The Complete Picture

RECAP

• The collection of Model instances (e.g. @tweets) is populated into views by Controllers
• Controllers are custom classes that inherit from ApplicationController
• Routes are the mechanism through which a given url (e.g. /tweets) invokes a particular method (e.g. index) in a controller (e.g. TweetsController)
• Routes are declared in the routes.rb file, using the simple resources method.

Code-Along

Let's modify the Twitter app to change the @tweets data set in the Controller before it passes it along to the view.

Solution From Class

EXERCISES

http://iexperience.github.io/exercises/7B.html