Ruby on Rails: Layouts and Rendering May 4th, 2015

  • By default, controllers in Rails automatically render views with names that correspond to valid routes
  • The rule is that if you do not explicitly render something at the end of a controller action, Rails will automatically look for the action_name.html.erb template in the controller’s view path and render it
    • If you want to render the view that corresponds to a different template within the same controller, you can use render with the name of the view 
      def update
 @book = Book.find(params[:id])
 if @book.update(book_params)
   redirect_to(@book)
 else
   render "edit"   # you can also use a symbol instead of a string  ... render :edit
 end
end
    • You can render a template from an entirely different controller from the one that contains the action code (relative to app/views)… 
      render "products/show"
  • You can render JSOn with render json: @product
  • Use the layout option to tell Rails to use a specific file as the layout for the current action: 
    render layout: "special_layout"
  • There are six asset tag helpers in Rails…
    • auto_discovery_link_tag (for RSS feeds)
    • javascript_include_tag
    • stylesheet_link_tag
    • image_tag … e.g.<%= image_tag “home.gif”, alt: “Go Home”, id: “HomeImage”, class: “nav_bar” %>
    • video_tag
    • audio_tag
  • Yield
    • Within the context of a layout, yield identifies a section where content from the view should be inserted 
      // Layout ...
<html>
 <head>
   <%= yield :head %>
 </head>
 <body>
   <%= yield %>
 </body>
</html>

// View ...
<% content_for :head do %>
 <title>A simple page</title>
<% end %>
 
<p>Hello, Rails!</p>
  • Partials
    • To render a partial as part of a view, you use the render method within the view 
      // Render a file named _menu.html.erb at that point within the view being rendered
<%= render "menu" %>

// ... or ...
<%= render "shared/ad_banner" %>

// ... or a partial using its own layout ...
<%= render partial: "link_area", layout: "graybar" %>
      • This would look for a partial named _link_area.html.erb and render it using the layout _graybar.html.erb
      • Note that layouts for partials follow the same leading-underscore naming as regular partials, and are placed in the same folder with the partial that they belong to (not in the master layouts folder)
    • You can pass-in local variables to make the partials even more powerful/customized … 
      // new.html.erb
<%= render partial: "form", locals: {zone: @zone} %>
// ... or ...
<%= render partial: "customer", object: @new_customer %>
// ... or if you have an instance of a model to render in the partial use the shorthand ...
<%= render @customer %>
// ... or render partials once for each object in a collection ...
<%= render partial: "product", collection: @products %>
// ... or with a custom local variable
<%= render partial: "product", collection: @products, as: :item %>

// _form.html.erb
<%= form_for(zone) do |f| %>
 <p>
   <b>Zone name</b><br>
   <%= f.text_field :name %>
 </p>
 <p>
   <%= f.submit %>
 </p>
<% end %>

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