Can someone explain where/why this might be used? Or is it just for fun?
[1]: https://github.com/hasura/graphql-engine/
OTOH, having dug into PostGraphile a bit, I personally wouldn't advocate for pushing so much backend logic into the DB.
Like, if you decide to do auth and TOTP in the DB, you'll end up implementing it in PL/pgSQL. Writing core security logic in a less-familiar language feels like it adds risk.
Also, for smaller projects your backend is often just a single server, so moving auth in into the DB doesn't save you from managing distributed state.
I do agree about making sure you have experience writing PL/pgSQL and would also add that you should make sure you have a good test-driven environment when writing code in the db.
Not really? Postgres (as well as other rdbms) support many other languages - I don't see many good reasons to insist on pl/pgSQL for uses like these?
Both python, perl and TCL are part of the standard distribution in addition to pl/pgSQL.
I could use plv8, but there's a more subtle preference here for JS to wrap SQL, rather than the reverse (plus tooling is less convenient, e.g. if you're writing Typescript).
My rule of thumb is: SQL great, PL not so much.
Agreed.
However, I don't see why not use one of the other mature "real" extension languages other than pl/pgSQL.
As for typescript, maybe there's (distant) hope:
I use graphile and didn't want to have to implement a resolver in JavaScript, keeping logic and integrity of auth systems in the database.
I ultimately switched to native PG. There were known memory leaks in plv8 and eventually after learning pl/pgsql it became more natural and clean, plus AWS at the time didn't support plv8 which was another incentive not to use language extensions