Delete data or just flag it as deleted?

I'm building a website that lets people create vocabulary lessons. When a lesson is created, a news items is created that references the lesson. When another user practices the lesson, the user also stores a reference to it together with the practice result.

My question is what to do when a user decides to remove the lesson?

The options I've considered are:

• Actually delete the lesson from the database and remove all referencing news items, practise results etc.
• Just flag it as deleted and exclude the link from referencing new开发者_运维问答s items, results etc.

What are your thoughts? Should data never be removed, ala Facebook? Should references be avoided all together?

By the way, I'm using Google App Engine (python/datastore). A db.ReferenceProperty is not set to None when the referenced object is deleted as far as I can see?

Thanks!

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Where changes to data need to be audited, marking data as deleted (aka "soft deletes") helps greatly particularly if you record the user that actioned the delete and the time when it occurred. It also allows data to be "un-deleted" very easily.

Having said that there is no reason to prevent "hard deletes" (where data is actually deleted) as an administrative function to help tidy up mistakes.

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Marking the data as "deleted" is simplest. If you currently have no use for it, this keeps everything in your database very tidy and makes it easy to add new functionality.

On the other hand, if you're doing something like showing the user where their "vocabulary points" came from, or how many lessons they've completed, then the reference to soft deleted items might be necessary.

I'd start with the first one and change it later if you need to. Here's why:

• If you're not using soft deletes, assume they won't work in the way that future requests actually want them to. You'll have to rewrite them anyway.
• If you are using them, assume that nobody is using the feature which uses them. Now you've done a lot of work and tied yourself into maintenance of something nobody cares about.
• If you create them, you'll find yourself creating a feature to use them. See the above.
• If you don't create them, you can always create them later, once you have better knowledge about what the users of your system really want.

Not creating soft deletes gives you more options going forward. Options have value. Options expire. Never commit early unless you know why.