ORMs are extremely simple to implement. I've written them a few times in Java for simple things. Primarily you need something equivalent to reflection so you can read from and inject into any properties that an object might contain. Does Nim have this kind of feature set?

I've never written one, I always thought it's one of those things that sound simple but actually require a lot of careful thought and design.

Nim doesn't do reflection, but it has some of the best metaprogramming features including static introspection tools which are far superior to reflection IMO.

It just takes some opinions. If you haven't developed any yet just take someone else's opinions. Eloquent is a good start for where to look. The QueryBuilder frame is a nice platform that makes available many nice features.