I just switched one of my systems over to NixOS from Arch and so far it seems interesting. One question I had is regarding the nix-shell. So I get the basic concept of it and that it allows creating a shell that has packages installed with that shell making ideal for dev environments. I’ve even seen talks where the suggest nix-shells over docker/podman, my question is how is persistent data (like databases) handled?
No, you won’t lose anything. However do be aware that unless you specifically configure different data directories using the same DBMS in multiple projects will use the same underlying data files.
Typically this won’t be a problem, and you can just create different logical databases if necessary.