filterable.rb

module Filterable                                                                
  extend ActiveSupport::Concern    
  
  module ClassMethods                                                            
     def filter(filtering_params)                                                 
       results = where(nil)                                                       
       filtering_params.each do |key, value|                                      
         results = results.public_send(key, value) if value.present?              
       end                                                                        
       results                                                                    
     end                                                                          
   end                                                                            
end