Rails: Where "params" is defined?

Question

I use params in my controller like this:

class ProductsController < ApplicationController
  def create
    @product = Product.new(params[:aircon])
    ...
  end
end

Is params an attribute of ApplicationController ? I guess not, because it does not have the @ prefix. So, what actually params is ? Can I use it in any custom method in ProductsController ?

Answer 1

It's defined in ActionController::Metal. ApplicationController inherits from ActionController::Base, which inheirts from ActionController::Metal. If you look at the Rails API at http://api.rubyonrails.org/, you will find params is just a function that returns the paramaters of the request object.

Answer 2

The parameters are actually being parsed in middleware called ActionDispatch::ParamsParser. The params function in ActionController::Metal is a wrapper for this.