instiki/vendor/rails/railties/lib/rails_generator/generators/components/migration/templates/migration.rb

class <%= class_name.underscore.camelize %> < ActiveRecord::Migration
  def self.up<% attributes.each  do |attribute| %>
    <%= migration_action %>_column :<%= table_name %>, :<%= attribute.name %><% if  migration_action == 'add' %>, :<%= attribute.type %><% end  -%>
  <%- end %>
  end

  def self.down<% attributes.reverse.each  do |attribute| %>
    <%= migration_action == 'add' ? 'remove' : 'add' %>_column :<%= table_name %>, :<%= attribute.name %><% if migration_action == 'remove' %>, :<%= attribute.type %><% end  -%>
  <%- end %>
  end
end