Question

is there any way to persist (preserve) parameters in Rails controller? It should be passed to every action, then to every view and every link.

Example situation:
I have entity A with its controller. Besides, I have another entity B which is dependent on A. I need to access the “parent” A entity very often, so I’d like to have it still as

http://some_url/b_controller/b_action?a_entity=xyz

Answer 1

You should be able to do everything from your controller, using a combination of before_filter and default_url_options :

class MyController < ApplicationController

  before_filter :set_a_entity

  def set_a_entity
    @a_entity = params['a_entity']
    # or @a_entity = Entity.find(params['a_entity'])
  end

  # Rails 3
  def url_options
    {:a_entity => @a_entity}.merge(super)
  end

  # Rails 2
  def default_url_options
    {:a_entity => @entity}
  end

end

This doesn’t solve the problem of setting the initial value of @a_entity, but this can be done from anywhere (view, controller, etc).

If you want this parameter passed around in multiple controllers, you can replace MyController < ApplicationController with ApplicationController < ActionController::Base and it should work as well.

Hope this helps.