module PowerTools::ActiveRecord::SetAssociationWithHash
  def association_hash_writer(*associations)
    unless generated_methods?
      define_attribute_methods
    end
    
    associations.each do |a|
      unless respond_to?("#{a}_with_hash_writer=")
        define_method "#{a}_with_hash_writer=" do |attributes|
          if attributes.is_a?(Hash)
            if existing = send("#{a}")
              existing.update_attributes(attributes)
            else
              send "build_#{a}", attributes
            end
          else
            send "#{a}_without_hash_writer=", attributes
          end  
        end
             
        alias_method_chain "#{a}=", :hash_writer
      end
    end
  end
end