Rails: Up and Running, 2nd Edition

Tying Controller Data to the View

In MVC, the view needs to render any data the controller provides. That data may come from model logic, the session, or any other source. Regardless of where the data comes from, in Rails, instance variables in the controller are available to the view. Let’s try setting a variable called @welcome_message in the controller:

class GreetingController < ApplicationController
   def index
     @welcome_message = "Welcome to your first Rails application"
   end
end

Now, display the new message in the view by adding a Ruby expression between the <%= and %> tags. Rails renders the value of the expression within these tags, just as if the value of the expression had been printed in place. Here’s a view that prints your welcome message as a level one heading:

<h1><%= @welcome_message %></h1>

Reload. You'll see the output from the view, with the message you created in the index method. In Example 1-1, you rendered your view within the controller. Here, you built an HTML.ERB template. Your HTML tags provided static structure and style, and your Ruby code provided dynamic content—in this case, a variable set within the controller. That’s MVC.

Expressions and Scriptlets

When you’re embedding Ruby code within a view template, you’ve got two options. Scriptlets are Ruby code placed between the <% and %> tags. Scriptlets run Ruby code without printing the results. You will often use a scriptlet to loop through the elements of a Ruby array, for example. Expressions are Ruby expressions ...