This module is an official contributed module for the Drupal Commerce. When the Drupal Commerce is released, I heard so many people complaining about the separation between Product and Product Display in Drupal Commerce module. So, this module is created in order to solve that problem. This module can simplify the Product Display creation process by providing option the create it at the same time with Product creation.
Drupal 7 has a very great Ajax framework which allow us to use Ajax feature when we build the module. One of Ajax feature that we can develop in Drupal module is Ajax dropdown list. In this tutorial, we will see how create it. For the example, we will create two dropdown list, one contains the list of provinces which already populated at page load, and the other one will be filled dynamically with the cities list based on the selected item in province dropdown list.