Nested layouts on Rails ~> 3.1

02 Feb 2013

Nested layouts on Rails ~> 3.1

tl;dr

Put this in your ApplicationHelper:

def inside_layout(parent_layout)
  view_flow.set :layout, capture { yield }
  render template: "layouts/#{parent_layout}"
end

Then create inner templates (mine are usually for a controller) that look like this:

<%= inside_layout "application" do %>
  <p>before template</p>
  <%= yield %>
  <p>after template</p>
<% end %>

Works in Haml, too.

Yet another way to nest your layouts

Nested layouts is a topic that has been discussed to death, both in the official Rails views guide and appears to have confused many different people on Stack Overflow.

The “nested layouts” from the Rails view guide have always baffled me. Ultimately, the idea that they claim is best practice boils down to setting up a bunch of custom yield calls in your application layout and then using the child layouts to call content_for a bunch of times before rendering the application layout.

This week, I got asked about setting up nested layouts by someone who tried to read the Rails guide and just got confused, so I went to see if there was a better way. I ran across this blog post, and that led to a gist demonstrating layout nesting via partials. While those options did actually work, I didn’t like the semi-magic call to parent_template at the end of the first option, and I didn’t like the requirement of a partial in the second.

After beating my head against nested yield calls for a while, I managed to come up with a two-line helper method that takes a block with the “inner” layout inside it. I’m pretty happy with how it came out.

The inside_layout method just takes the name of the parent layout and a block with the inner layout contents. The inner layout must call yield, as usual, where the action template should be inserted. Since you read past the tl;dr, I’ll even explain what’s going on for you! :D

  def inside_layout(parent_layout)
    view_flow.set :layout, capture { yield }
    render template: "layouts/#{parent_layout}"
  end

I didn’t know this before, but Rails 3.1+ views (and helpers) all have a view_flow object available to them that manages all of the various content_for sections. Using that object, we swap out what will be inserted when the next template rendered calls yield. What we put in instead is the result of calling capture with the block that was passed to our helper. That method returns a string with the result of rendering the block. Finally, we simply render the parent layout, knowing that when it calls yield, it will get the result of rendering our entire inner layout’s block. Pretty sweet.

André.Arko.net