Rails: How To Create Custom Validations

Often our model objects leaning toward to be confused or noisy, due to validations DSLs. Imagine a class Answer, with an attribute, that should be exactly a string representation of a boolean. Ok, I know it’s an odd example, but: it’s trivial enough to make this example clear, and.. It happened to me to deal with this situation. :-P

class Answer %w( true false ), :message => "Should be exactly true or false." end

Now, we try to clean-up a bit this code. First, create a file named validations.rb into lib, then copy and paste this code:
module ActiveRecord module Validations module ClassMethods @@boolean_values = %w( true false ) @@validates_boolean_msg = "Should be exactly #{@@boolean_values.join(' or ')}."

      # Check if the value is a boolean: <tt>true</tt> or <tt>false</tt>.
      def validates_boolean(*attr_names)
        configuration = { :message   =&gt; @@validates_boolean_msg,
                          :in        =&gt; @@boolean_values }

       configuration.update(attr_names.pop) if attr_names.last.is_a?(Hash)
       validates_inclusion_of attr_names, configuration
      end
    end
  end
end

Then we are going to add the following line at the end of environment.rb
require ‘validations’

Let’s clean the code:
class Answer

Is it better? Maybe.. ;-)