rails prepend_view_path of mountable engine

Question

In one hand, I have a mountable engine let's say Front Front contain my assets and couple of pages It's isolated from MainApp. I don't want it to touch the main app.

In the other hand I want my MainApp using layout and partial of the Front. So I setup the layout this way :

class ApplicationController < ActionController::Base
    layout 'front/application'
end

But the front/application refer to engine partial directly, because of isolation, like this

render 'header' # front/ prefix is not required

So the MainApp views try to load app/views/application/header instead of app/views/front/application/header

To fixe this I put a prepend_view_path like this :

class ApplicationController < ActionController::Base
    layout 'front/application'
    before_filter :prepend_front
protected
    def prepend_front
       prepend_view_path "app/views/front"
    end
end

But this doesn't work because engine path point into the vendor. The engine add it self this to the prepend path list : ~/main_app/vendor/private_gems/front-0.0.2/app/views And my preprend_front method create this : ~/main_app/app/views/front

I tryed to prepend by force the correct path (but it looks so dirty) :

prepend_view_path "#{Rails.root}/vendor/private_gems/front-0.0.2/app/views/front"

I doesn't work, just crash the app ...

And I'm stuck here. Maybe my design is wrong?

Answer 1

The answer from Jack is perfect except if you want to do this inside the Rails engine (for example if your engine itself has 'themes' that require a different load path). In this case the prepend_path and append_path are not appropriate since you are going to want to insert your new load path before the engines default load path but after the applications load path.

A solution to this (only tested in Rails 3.2) is to add the following to your engines /lib/my_engine.rb file:

config.after_initialize do
  my_engine_root = MyEngine::Engine.root.to_s
  paths = ActionController::Base.view_paths.collect{|p| p.to_s}
  paths = paths.insert(paths.index(my_engine_root + '/app/views'), my_engine_root + '/app/views/themes/my_theme')
  ActionController::Base.view_paths = paths
end

The new load path my_engine_root + '/app/views/themes/my_theme' will now be just before your engines standard load path my_engine_root + '/app/views'