What's the correct way to run one controller action from another controller action without an HTTP redirect?

Question

I'd like to be able to dispatch from one controller action to another conditionally, based on a combination of query parameters and data in the database.

What I have right now is something like:

class OldController < ApplicationController
  def old_controller_action
    if should_use_new_controller
      new_params = params.dup
      new_params[:controller] = "new_controller_action"
      redirect_to new_params
      return
    end
    # rest of old and busted
  end
end

class NewController < ApplicationController
  def new_controller_action
    # new hotness
  end
end

This works just fine, but it issues an HTTP redirect, which is slow. I'd like to be able to do this same thing, but within the same HTTP request.

Is there a clean way to do this?

Edit: The bounty will go to someone who can show me a clean way to do this that leaves the controllers and their actions relatively untouched (other than the redirect code itself).

Answer 1

Instead of calling code across actions, extract the code to lib/ or something, and call that code from both controllers.

# lib/foo.rb
module Foo
  def self.bar
  # ...
  end
end

# posts_controller
def index
  Foo.bar
end

# things_controller
def index
  Foo.bar
end

Answer 2

Create an instance of the controller class:

@my_other_controller = MyOtherController.new

Then call methods on it:

@my_other_controller.some_method(params[:id])

I prefer the module idea, but this should do the trick.

You can also pass parameters as a whole from another controller:

@my_other_controller.params = params