remove_validation.rb

ActiveRecord::Base.class_eval do
  class << self
    # Ugly bit of metaprogramming to remove an existing validation
    # @param type of validation. ex. :validates_uniqueness_of
    # @param name of attribute to be validated. ex. :email
    def remove_validation type, name
      @validate_callbacks.reject! do |back|
        proc = back.method
        if proc.is_a?(Proc)
          # Returns the name of method the proc was declared in
          method = eval("caller[0] =~ /`([^']*)'/ and $1", proc.binding).to_sym rescue nil 
          attrs = eval("attrs", proc.binding) rescue nil
          if method == type
            if attrs.include?(name) && attrs.length > 1
              eval("attrs.delete(#{name})", proc.binding)
              false
            elsif attrs.include?(name)
              true
            else
              false
            end
          end
        else
          false
        end
      end
    end
  end
end