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Rails 3 does not render a partial for a specific format — resolving the issue

There is a problem in Rails 3: if you want to render a partial in HTML format in an AJAX request, you won't be able to. In this post, I describe how to avoid this problem.

Andrei Kaleshka
Andrei Kaleshka · 1 min read

Problem

For example, you make an AJAX request to the server in JSON format. Assume we have to render a partial in the controller or view and return it in a JSON object. In the view, you may have code like this:

  • Rails3 view
<%= {:form => render('form')}.to_json %>

In Rails 2, you could pass the format as an option to the render function, and it fixed the problem:

  • Rails2 view
<%= {:form => render(:partial => 'form', :format => :html)}.to_json %>

But in Rails 2, this is not working. There is a fix for this issue, and it has been merged into master. So in Rails 4, it will indeed work, and the method signature will look like this:

  • Rails4 view
<%= {:form => render(:partial => 'form', :formats => [:html])}.to_json %>

To enable this feature in Rails 3, you can make a monkey patch: just create a new file, config/initializers/renderer.rb, in your application and paste this code there:

  • Monkey patch for Rails 3
class ActionView::PartialRenderer
  private
  def setup_with_formats(context, options, block)
    formats = Array(options[:formats])
    @lookup_context.formats = formats | @lookup_context.formats
    setup_without_formats(context, options, block)
  end

  alias_method_chain :setup, :formats
end
rails3render

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