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action-view-demo.md

ActionView Demo

In this demo we will:

  • Learn about ActionView including:
    • templates, partials and layouts
    • response formats
    • helpers

1. Prerequisites

2. Starting from rails new

Let's create our Rails application and open the code in the Visual Source Code IDE.

rails new action_view_demo
code action_view_demo

Let's open the integrated terminal using Ctrl-` (backtick) and notice that this places the prompt in the action_view_demo directory. So we can just commit source code as follows:

git add .
git commit -m'rails new action_view_demo'

3. Generating a User

This time we're going to generate our User scaffold first:

rails generate scaffold user username:string first_name:string last_name:string bio:text bicycles:integer gpa:float birth_date:date account_expiration:datetime earthling:boolean

Then we'll set our root route by making the following change to config/routes.rb

# config/routes.rb
Rails.application.routes.draw do
  root 'users#index' # ADD THIS LINE!
  resources :users
end

Finally, we'll migrate the database and push (commit) our code.

rails db:migrate
git add .
git commit -m'Generate a User scaffold, set the root route and migrate the database'

4. Templates, Partials and Layouts

Let's examine the app/views/users/new.html.erb template, which references a partial that defines an HTML form in app/views/users/_form.html.erb.

If we start the Rails server (run: rails server in our console), visit the new User view in a browser at http://localhost:3000/users/new and view the page source we see more HTML than is contained in the template and partial combined.

The remainder of the HTML is generated as a default layout by the scaffold generator and contained in app/views/layouts/application.html.erb. Together, these files define the response sent back to your browser when a specific route is requested.

5. Response Formats

Notice that several methods in app/controllers/users_controller.rb contain respond_to blocks. Notice also the comments associated with each controller method which the Rails scaffold generator produced. For example, the create method is preceded by these two comment lines:

# POST /users
# POST /users.json

The comments indicate that the scaffold generated the code needed to process requests in both HTML and JSON formats. Let's add an XML format by adding a file named app/views/users/show.xml.builder with these contents:

# app/views/users/show.xml.builder
xml.user do
  @user.attributes.each { |k, v| xml.tag!(k, v) }
  xml.url(user_url(@user, format: :xml))
end

Now, with the server still running, let's add a User by completing the New User form if you haven't already added one, and view all three formats:

Let's make note via the comment above the show method in the UsersController that we've added an XML formatted view for that route:

# app/controllers/users_controller.rb
...
# GET /users/1
# GET /users/1.json
# GET /users/1.xml
def show
end
...

Finally, we'll commit our changes.

git add .
git commit -m'Add an XML format for users#show view'

6. Helpers

We noticed the form_with method in the Ruby embedded in the app/views/users/_form.html.erb partial. ActionView::Helpers defines a myriad of helper methods available to assist in rendering valid markup. For example:

  • form_with and field specific helpers defined in ActionView::Helpers::FormHelper
  • pluralize helper defined in ActionView::Helpers::TextHelper
  • date_select and datetime_select helpers defined in ActionView::Helpers::DateHelper
  • javascript_pack_tag and stylesheet_link_tag helpers from the application layout defined in ActionView::Helpers::AssetTagHelper

7. Helping Helpers

The default markup produced by the generated scaffolding is fine for general purposes but we'd like to tweak those a bit.

First, we defined the GPA field as a floating point (decimal or "float") value but the scaffold produced a text field. We know FormHelper can produce a number_field for integer values. We can use that for the GPA field and set a step attribute to 0.1, a maximum value of 4.0, and a minimum of 0.0 to make it easy for users to input reasonable values. To do so, we'll make this change to the file app/views/users/_form.html.erb:

# app/views/users/_form.html.erb
...
<div class="field">
  <%= form.label :gpa %>
  <%= form.number_field :gpa, max: 4.0, min: 0.0, step: 0.1 %>
</div>
...

Next, the generator does not understand that our birth_date field needs to accommodate the oldest living human. So the 10 year range the helper includes by default is not going to get the job done. I think I read that the oldest living human is about 115 years old. Let's add a five year buffer just in case they discover our app and what to sign up! We'll also add code to ensure that users are at least 18 years old and will set the default value to equal to the birth date of people turning 18 today. We can make the changes below to accomplish that:

# app/views/users/_form.html.erb
...
<div class="field">
  <%= form.label :birth_date %>
  <%= form.date_select :birth_date, start_year: 120.years.ago.localtime.year, end_year: 18.years.ago.localtime.year, selected: 18.years.ago.localtime %>
</div>
...

Finally, let's set the account expiration timestamp to be one year from now and specify an AM/PM time format. Here's how we accomplish that:

# app/views/users/_form.html.erb
...
<div class="field">
  <%= form.label :account_expiration %>
  <%= form.datetime_select :account_expiration, ampm: true, selected: 1.year.from_now.localtime %>
</div>
...

Looking good! Visit the New User view and notice the effect of the changes. This is a good place to commit the code!

git add .
git commit -m'Tweak gpa, birth_date and account_expiration input fields'

?. Bootstrap

Further Reading:

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