Using Helpers

Earlier we said that it’s OK to put code in templates. Now we’re going to modify that statement. It’s perfectly acceptable to put some code in templates, because that’s what makes them dynamic. However, it’s poor style to put too much code in templates. Three main reasons for this stand out. First, the more code we put in the view side of our application, the easier it is to let discipline slip and start adding application-level functionality to the template code. This is definitely poor form, because we want to put application components in the controller and model layers so that it is available everywhere. This will pay off when we add new ways of viewing the application.

The second reason is that html.erb is basically HTML. When we edit it, we’re editing an HTML file. If we have the luxury of having professional designers create our layouts, they’ll want to work with HTML. Putting a bunch of Ruby code in there just makes it hard to work with.

The final reason is that code embedded in views is hard to test, whereas code split out into helper modules can be isolated and tested as individual units. Rails provides a nice compromise in the form of helpers. A helper is simply a module containing methods that assist a view. Helper methods are output-centric and exist to generate HTML or XML, or JavaScript, which are helpers that extend the behavior of a template.

Your own helpers

By default, each controller gets its own helper module. Additionally, there is an application-wide helper named application_helper.rb. Rails makes certain assumptions to help link the helpers into the controller and its views. While all view helpers are available to all controllers, it often is good practice to organize helpers. Helpers that are unique to the views associated with the ProductController tend to be placed in a helper module called ProductHelper in the file product_helper.rb in the app/helpers directory. You don’t have to remember all these details. The rails generate controller script creates a stub helper module automatically.

In Hiding an Empty Cart with a Custom Helper, we created one such helper method named hidden_div_if(), which enabled us to hide the cart under specified conditions. We can use the same technique to clean up the application layout a bit. Currently, we have the following:

<h3><%= @page_title || "Pragmatic Store" %></h3>

Let’s move the code that works out the page title into a helper method. Because we’re in the store controller, we edit the store_helper.rb file in app/helpers:

module StoreHelper
  def page_title
    @page_title || "Pragmatic Store" 
  end
end

Now the view code simply calls the helper method:

<h3><%= page_title %></h3>

Helpers for formatting and linking

Rails comes with a bunch of built-in helper ...