Special Case Pattern
Situation
Imagine there's a scheduled background process that fetches multiple orders from your database and tries to place/finalize them.
Like Amazon, we might have a complex process around placing orders that isn't as linear as we might think it would be.
In this case, we want a buffer period between the time when you click place order and when the order is really placed. This will make canceling an order an easy process (it avoids having to remove credit card charges and so on).
Given this scenario, we might be trying to process orders that have already been changed to an alternate state:
- Canceled order.
- Payment declined.
- The payment gateway is not responding, so we need to wait and retry later.
- Others!
Whenever you have multiple versions of these kinds of special cases, the Special Case pattern is here to save the day!
This pattern is just like the Null Object pattern but takes it that extra step.