How Can I Implement Conditional CSS Inclusion in Rails 3.1 Using Sprockets?

Conditional Asset Inclusion in Rails 3.1 with Sprockets

In the quest to optimize CSS rendering, many developers struggle with the challenge of selectively including CSS files based on specific conditions. This issue becomes pertinent when dealing with responsive layouts or ensuring compatibility across browsers.

In Rails 3.1, the asset pipeline provides a powerful mechanism for managing static assets. By default, the *= require_tree command in application.css includes all files within the assets/stylesheets directory. However, this approach may not suffice for conditionally including CSS files.

A Traditional but Clunky Solution

One workaround is to manually specify each CSS file, as illustrated:

*= require_self
*= require home.css
...
*= require blueprint/screen.css

While this method works, it becomes less practical as the number of CSS files increases.

Leveraging Separate Manifests and Organized Folders

A more elegant solution involves reorganizing the assets/stylesheets folder and using separate manifest files:

app/assets/stylesheets
+-- all
    +-- your_base_stylesheet.css
+-- print
    +-- blueprint
        +-- print.css
    +-- your_print_stylesheet.css
+-- ie
    +-- blueprint
        + ie.css
    +-- your_ie_hacks.css
+-- application-all.css
+-- application-print.css
+-- application-ie.css

Each category gets its own manifest file:

/* application-all.css */
*= require_self
*= require_tree ./all

/* application-print.css */
*= require_self
*= require_tree ./print

/* application-ie.css */
*= require_self
*= require_tree ./ie

The application layout file is updated accordingly:

 "all" %>
 "print" %>

<!--[if lte IE 8]>
    <%= stylesheet_link_tag "application-ie", :media => "all" %>
<![endif]-->

Remember to include the manifest files in config/environments/production.rb:

config.assets.precompile += %w( application-all.css application-print.css application-ie.css )

Image References

With this structure, caution is required when dealing with image references. One potential solution is to move images accordingly, ensuring consistent organization with the CSS files. Alternatively, one may opt to qualify the image path or leverage the SASS helper for image URLs.

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