Beyond Scaffolding

Full Stack Web WEBD-2007

Red River College

Introduction

Rails scaffolds allows us to quickly create database backed MVC applications. However, scaffolding has limitations, such as generic views, and an inflexibility to change in the model.

We need to learn how to enhance and modify our scaffolded MVC-bundles. To do this we will need to learn more about:

• How Rails routes URL requests to specific Controller Actions.
• How Rake Migrations can be used to update our Models.
• How Partials can be used to DRY* up our Views.

*DRY = Don’t Repeat Yourself (a.k.a. Single Point of Truth)

Objectives

This tutorial builds on the the blog engine tutorial.

Upon completion of this tutorial, you should be able to:

• Set a default Controller/Action for the root URL.
• Explore your application’s routing using Rake.
• Use the link_to helper to create links to named routes.
• Use migrations to add to our Model.
• Use View Partials to decrease repetition in our HTML/ERB.

Routing

Web applications accept URL requests from browsers and respond with webpages. When using Rails, these webpages are generated by calls to specific Controller Actions.

Rails uses a routing system to map URLs to specific Controller/Action pairs. The routes are defined in a routing file :

/config/routes.rb

Our blog’s posts Controller (generated via scaffolding) will show up in the routing as:

resources :posts

See the comments above each of the posts Controller’s Actions to see which URLs they map to.

Rails Routing

It is very important to understand how Rails maps URLs to particular Controller Actions:

Rails Routing from the Outside In

Setting a Root Route

By default the root URL of your Rails app maps to a welcome to Rails page. You can also map the root URL to a specific Controller/Action using routes.rb:

root to: 'posts#index'

The above route maps the root URL to the index Action of the posts Controller.

Viewing Routes

You can see your application routes using Rake from the command line:

rake routes > routes.txt

Now edit the routes.txt you just generated.

The columns in this file show the names of the routes, followed by their associated HTTP method and the URL, followed by the Controller/Action pair they map to.

Explore this file. Try to locate where the root route is defined, and note all the routes created for your posts controller.

Linking to a Named Route

Let’s say you want to add a link from the show view of your posts Controller to the new action.

Although you could hand-code the link in HTML it would be easier to use rake routes to determine the name of the new route (new_posts) and then use the link_to helper in the show.html.erb:

<%= link_to 'New Post', new_posts_path %>

Migrations

Rails Migrations allow us to make incremental changes to our Models.

To best understand Migrations please the Rails Guides page on Migrations.

Adding a New Column

Let’s say we want to add a new field to our Post model. Let’s say we want to record the ‘Awesomeness’ of each blog post. From the command line:

rails g migration add_awesomeness_to_posts awesomeness:string

This will create a new migration file in the db/migrate folder. Open and view this file to see the generated Migration.

To run this migration from the command line:

rake db:migrate

Updating the Views

Now that our blog Model has been updated we need to update our posts views.

In the new and edit views make use of a partial so that they do not repeat the same form code. We’ll add the following inside of the form_for block of the _form.html.erb file:

<p>
  <b>Awesomeness</b> <br />
  <%= f.text_field :awesomeness %>
</p>

The index and show views also need to be updated so that they display the new awesomeness field.

Constraining the Awesomeness

Let’s use a Model validation to constrain the possible choices for the Awesomeness:

ALLOWED_AWESOMENESS = [ "Awesome", "Almost Awesome", "Not Awesome" ]
validates_inclusion_of :awesomeness, :in => ALLOWED_AWESOMENESS

Using View Partials

Now that we’ve constrained the possible awesomeness choices, lets have the new and edit views use a dropdown select box for awesomeness. Again we will edit the _form.html.erb file to make this change.

This file is a partial, a piece of ERB-enhanced HTML that can be used by multiple views. If you look in either new.html.erb or edit.html.erb you will see the form partial loaded as follows:

<%= render 'form' %>

Within the partial itself we’ll change the text_field builder for awesomeness as follows:

<%= f.select :awesomeness, Post::ALLOWED_AWESOMENESS %>

Adding an Action to a Scaffold

Let’s add a new action to our blog’s posts Controller in routes.rb by modifying the resources command:

resources :posts do
  collection do
    get :stats
  end
end

Here we have added a stats Action that will respond to an HTTP GET request.

Adding an Action (Continued)

Now that we’ve configured the routing for the stats Action we need to add a new stats method to the posts Controller, along with a new stats.html.erb file in the app\views\posts\ folder.

I’ll leave this as an exercise to the reader.