Question

I have a simple database table that stores list of users who have subscribed to folders either by email OR to show up on the site (only on the web UI). In the storage table this is controlled by a number(1 – show on site 2- by email). When I am showing in UI I need to show a checkbox next to each of folders for which the user has subscribed (both email & on site).

There is a separate table which stores a set of default subscriptions which would apply to each user if user has not expressed his subscription. This is basically a folder ID and a virtual group name.

But, Email subscriptions do not count for applying these default groups. So if no “on site” subscription apply default group. Thats the rule.

How about a strategy pattern here (Pseudo code)

Interface ISubscription
  public ArrayList GetSubscriptionData(Pass query object)

Public class SubscriptionWithDefaultGroup
  Implement ArrayList GetSubscriptionData(Pass query object)

Public class SubscriptionWithoutDefaultGroup
  Implement ArrayList GetSubscriptionData(Pass query object)

Public class SubscriptionOnlyDefaultGroup
  Implement ArrayList GetSubscriptionData(Pass query object)

does this even make sense? I would be more than glad for receive any criticism / help / notes. I am learning.

Cheers

Answer 1

How about below. My choice is to use Decorator pattern. By the way I understood your problem, there are always default subscriptions and users can ADDITIONALLY subscribe for more. And Decorator is meant for this kind of ENHANCEMENTS while Strategy is for ALTERNATE IMPLEMENTATIONS.

Interface ISubscription
{
  public List<ISubscription> GetSubscriptions(Pass query object);
}

Public class DefaultSubscritions implements ISubscription {...}

Public class SubscribedSubscritions implements ISubscription 
{
   private ISubscription sub;

   public class SubscribedSubscritions(ISubscription in)
   {
     sub=in;
   }

   public List<ISubscription> GetSubscriptions(Pass query object) 
   {
     List<ISubscription> defaultSubs=sub.GetSubscriptions(...);
     List<ISubscription> additionalSubs=//retrieve the subscribed ones


     List<ISubscription> allSubs=//defaultSubs + additionalSubs

     return allSubs;
   }
}

Strategy allows you to replace something with an alternative implementation. Decorator transparently enhances objects.