Notes from David Vrensk on how to use Comatose's inline rendering with ActionMailer:

My app has to send out confirmation emails, and I use ActionMailer to do that. I want the site owner to be able to update (part of) the email template, so I put that part in a Comatose page. In the email template, I put

<% render :comatose => "email-text" %>

But this triggers the error

ActionView::TemplateError (undefined method `read_fragment' for #<Notifier:0x23849e4>) on line #15 of
app/views/notifier/order_confirmation.rhtml:
...
    #{RAILS_ROOT}/vendor/plugins/comatose/lib/support/inline_rendering.rb:30:in `render_cached_comatose_page'
    #{RAILS_ROOT}/vendor/plugins/comatose/lib/support/inline_rendering.rb:20:in `render_comatose'
    #{RAILS_ROOT}/vendor/plugins/comatose/lib/support/inline_rendering.rb:7:in `render'
    #{RAILS_ROOT}/app/views/notifier/order_confirmation.rhtml:15:in `_run_rhtml_order_confirmation'

(Notifier is my descendant from ActionMailer::Base.) Apparently, ActionMailer tells ActionView that it is the calling controller. That's duck typing for you.

I don't have a fix (don't know Rails or Comatose well enough yet), but I have a work-around if anyone is interested:

1. Comatose only tries to call #read_fragment if it uses fragment caching. So, turn of fragment caching for this call:

   <% render :comatose => "email-text", :use_cache => false %>
   

2. Comatose will now try to render as usual, passing the original request parameters to the Page. But to do this, it has to pick up the params from the controller. Again, the controller is unavailable, but this page doesn't need the params anyway, so I fake them by adding

   def params Hash.new end

to Notifier, my ActionMailer::Base descendant. And now, all is good. Hacky, but good.

Thanks David!