Just want to suggest that if you're interested in doing this in the future, some investment in defining interfaces up front is worth doing. I took a quick look at the codebase and it looks like mongo is "in there pretty good"[0] without any abstraction to make it easily shimmable.

Just a little specification around the that interface (Trait) will go a long way to making other backends possible and should make it much easier to know and manage the API contract a capable database must provide.

[0]: https://github.com/revoltchat/delta/blob/master/src/database...