Sohan's Blog

Things I'm Learning

The Perils of Soft Delete

Often times, applications cannot get rid of the database records for business rules. For example, if you are a cable TV provider, you might have a customer calling you to stop the National Geographic Channel subscription from next month. Ideally you would like to delete this record, but you can’t do it until the effective date:( If you delete it, the next invoice will not be able to charge for this channel, although it’s still being used.

In such scenarios, its common to fall back to a soft delete model. As an example, here’s a little code:

This code looks simple and harmless at a first sight. But, as you develop your app, you’ll run into a lot of issues from this. Here’s a short list:
  1. You need to take care of cascading soft delete, for example, cancelling a customer’s subscription needs to cascade down to all channels and other objects under it.
  2. Whenever, you are listing the current subscriptions of a customer, you need to filter out the ended ones.
  3. You need to figure out a strategy to periodically clean the ended subscriptions so that your database is not filled with outdated data.
  4. If you have a business key used as a primary key as well, you will be in trouble if an ended subscription is restarted.
  5. Your code will eventually have a lot of if-else blocks to apply changes to only on active objects.
So, what is the solution? Its best to avoid them as much as possible. Richard Dingwall has a detailed blog post on some alternative techniques to avoid soft-delete. But if you have to have soft delete, as shown in the example, its worth remembering the aforementioned points.