Pulling avatars from twitter in a Rails App »

Passing a parameter to a before filter

Creating a controller filter that accepts a parameter is less than obvious as I found today while trying to add more than basic authentication to a controller.

Turns out that you need to do it like this :

before_filter :only => [:create, :update, :destroy] do |controller|
controller.filter_function(parameter)
end

rather than allowing a parameters array to pass into the before_filter function which would be nice.

Tags: , ,

This entry was posted on Friday, December 5th, 2008 at 11:32 am and is filed under Ruby on Rails. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

2 Responses to “Passing a parameter to a before filter”

  1. Cassiano D'Andrea Says:
    January 20th, 2009 at 5:09 pm

    Hi. After reading your post I came out with:

    class ApplicationController < ActionController::Base
  #################################################
  def self.parameterized_before_filter(filter_name, *args)
    options = args.extract_options!

    self.before_filter(options) { |controller| controller.send(filter_name, *args) }
  end

  #################################################
  # Sample usage with 2 parameters.
  parameterized_before_filter :my_filter, 'param1', 'param2', :only => :create

  #################################################
  # Sample usage passing a hash as a parameter value.
  parameterized_before_filter :my_filter, 'param1', 'param2',
                                            { :param3 => :value3 }, :only => :create

  #################################################
  # The filter itself.
  def my_filter(*args)
    puts args.inspect
  end
end

    How do you like it? Why doesn’t Rails provide such method out of the box?

    One might also add :parameterized_before_filter directly to ActionController::Base, or even replace the original :before_filter (using :alias_method_chain).

    Thanks for sharing the tip.

  2. andrew Says:
    January 20th, 2009 at 5:40 pm

    Hi Cassiano,
    I fixed your comment :) Wordpress was obviously screwing up your previous attempts.
    The parameterized_before_filter is great much more thought out than my simple attempt.
    I’m not sure why rails doesn’t provide such a method already as it is pretty useful, i guess though that ruby lets you do it pretty easily anyway if in a non newbie friendly way. If you find out the reason please let me know.

Leave a Reply