fix: handle queries on non-existing table gracefully

[taimoorzaeem]

Add new TableNotFound error and add json error
message for this error. Closes #3697.

(Couldn't think of a better changelog/commit message. Feel free to suggest a new/better message).

[steve-chavez]

Seeing the change in the tests output, I think this should also be listed in ### Changed.

This also means that we should release it on the upcoming major.

[wolfgangwalther]

Does that mean you would not consider backpatching this?

Personally, I don't think this needs to be explicitly mentioned. It's an error condition that nobody relies on. This only comes up when they do something wrong - and they get a better error now. So this is hardly breaking any existing workflows, right?

(maybe I missed the relevant test output change, though - I assume it's about the 400 -> 404, from no foreign key relationship -> no table)

[steve-chavez]

Does that mean you would not consider backpatching this?

Yeah, I was thinking no backpatch. Just to be extra careful.

So this is hardly breaking any existing workflows, right?

I know some users that rely on table requests with no resource embedding being fast (in presence of slow relationships loads), if that has changed (test mentioned on #3869 (comment)) then it would certainly break existing workflows.

[wolfgangwalther]

I know some users that rely on table requests with no resource embedding being fast (in presence of slow relationships loads), if that has changed (test mentioned on #3869 (comment)) then it would certainly break existing workflows.

So the way we used to think about this was, that "hitting the database" is the slow part and "returning early with information from schema cache" was the fast path, right?

But now this logic is turned around - and schema cache is potentially slow?

I see why you would not want to backpatch this, agreed.

[steve-chavez]

Now that we rely on the schema cache for simple table filters, we need to make sure these requests are fast when a schema cache load for relationships is slow (#3046).

There's a test that validates the above behavior (a request with resource embedding is blocked until the schema cache finishes loading):

postgrest/test/io/test_big_schema.py

Lines 10 to 34 in 52591c0

	def test_requests_wait_for_schema_cache_reload(defaultenv):
	"requests that use the schema cache (e.g. resource embedding) wait for the schema cache to reload"
	env = {
	**defaultenv,
	"PGRST_DB_SCHEMAS": "apflora",
	"PGRST_DB_POOL": "2",
	"PGRST_DB_ANON_ROLE": "postgrest_test_anonymous",
	"PGRST_SERVER_TIMING_ENABLED": "true",
	}
	with run(env=env, wait_max_seconds=30) as postgrest:
	# reload the schema cache
	response = postgrest.session.get("/rpc/notify_pgrst")
	assert response.status_code == 204
	postgrest.wait_until_scache_starts_loading()
	response = postgrest.session.get("/tpopmassn?select=*,tpop(*)")
	assert response.status_code == 200
	plan_dur = parse_server_timings_header(response.headers["Server-Timing"])[
	"plan"
	]
	assert plan_dur > 10000.0

We need an additional test that asserts that a table request (with no resource embedding) finishes in a short plan_dur after reloading the schema cache (calling /rpc/notify_pgrst in the test).

[wolfgangwalther]

Does that mean you would not consider backpatching this?

Personally, I don't think this needs to be explicitly mentioned. It's an error condition that nobody relies on. This only comes up when they do something wrong - and they get a better error now. So this is hardly breaking any existing workflows, right?

(maybe I missed the relevant test output change, though - I assume it's about the 400 -> 404, from no foreign key relationship -> no table)

[taimoorzaeem]

One last concern, we are still using NotFound error in a couple places, which returns an empty error json:

postgrest/src/PostgREST/ApiRequest/Types.hs

Line 82 in e2dd435

| NotFound

postgrest/src/PostgREST/Error.hs

Line 135 in e2dd435

toJSON NotFound = JSON.object []

This seems fine for now, but maybe should be improved later (add error msg, details etc) for better UX?