Database craft

The database holds state; the application holds logic. Postgres enforces structure, each action runs as one statement whose own locks make it atomic, a derived value is written with its input, and jobs do the rest.

These rules assume Postgres. Follow the project's database policy where it is stricter, and its migration tooling for schema changes. Ask before introducing a pattern these rules ban, such as a trigger, a manual lock, or a serializable transaction; restructure first.