How to remove validation using instance_eval clause in Rails?

Question

I would like to enhance existing class using instance_eval. There original definition contains validation, which require presence of certain fields, ie:

class Du         


        

Answer 1

One solution is to extend validates :

#no need of instance_eval just open the class
class Dummy < ActiveRecord::Base
  #validates :field, :presence => true 

  def self.validates(*attributes)
    if attributes.first == :field #=> add condition on option if necessary
      return # don't validate
    else
      super(*attributes) #let normal behavior take over
    end
  end
end

And no that's not monkey-patching but extending or decorating a behavior. Rails 3.1 is built on the idea of "multi- inheritance" with module inclusion, specifically to allow this kind agility.

update #2

One caveat is you must load the class with the redefined validates method before the gem containing the call to validates. To do so, require the file in config/application.rb after require "rails/all" as suggested in the railsguides. Something like that :

require File.expand_path('../boot', __FILE__)

require 'rails/all' # this where rails (including active_record) is loaded
require File.expand_path('../dummy' __FILE__) #or wherever you want it

#this is where the gems are loaded...
# the most important is that active_record is loaded before dummy but...
# not after the gem containing the call to validate :field
if defined?(Bundler)
  Bundler.require *Rails.groups(:assets => %w(development test))
end

Hope it works now!