Does YAGNI apply to database design?

Question

In code, it's generally pretty easy to add new classes to provide additional functionality and such. I have a fairly good understanding of refactoring code and what's involved so YAGNI generally makes sense to me.

What I'm not as familiar with is working with and updating a relational database once it's deployed. I'm developing a little pet project that I'm planning on practicing Release Early, Release Often on and I'm wondering if I should be considering data that won't be used in the initial release, but is on the planned features list? Is it as easy to add tables and tweak schemas around as it is to add new classes? Or should I try to have tables set up for things I could conceivably use, but aren't planning to in the immediate future?

Answer 1

This is an excellent question. I've personally found that modifying a database schema and converting all the data to the new representation to be far more difficult than refactoring code. So much so, in fact, that whenever I start a project that will use a new database I always take time before I sit down and write any code to get my spec as thorough as possible. What this often entails is anticipating features and incorporating support for them into the database, even if I don't plan on immediately implementing them.

You might be able to be a bit more nimble with database refactoring if you're using a framework or other similar layer that provides a mechanism for altering the database, but if you're writing straight SQL then I would recommend investing a modest amount of time designing and implementing a schema that is less likely to require changing in the future.

Answer 2

If you have good testing that hits the database, I would extend YAGNI to your database design.

In general, it is easy to add columns and tables, and less easy to remove or modify them significantly. Take that into consideration when you design tables (i.e. if a customer can have multiple users, don't add userid to your customers table. Do it right the first time).