Re: Lookup tables

[Michał Kłeczek <michal@xxxxxxxxxxx>]

On 6 Feb 2025, at 22:03, Peter J. Holzer <hjp-pgsql@xxxxxx> wrote:

On 2025-02-04 22:41:38 +0100, Thiemo Kellner wrote:

I might see what you want to point out. E.g. the table is COLOURS. The
rec with id 1 is RED, the one with id 2 is BLUE, 3 is GREE and so on.
Now you load these values into the dropdown box that sports RED, BLUE,
GREE and so on. While someone selects GREE, there is a maintenance
release changing GREE to YELLOW. So when that someone sends the
selection by id to the backend, not GREE is selected but YELLOW.

I fail to see why use of a surrogate key is the problem here.

Either changing the color from GREE to YELLOW makes sense or it doesn't.

If it doesn't make sense, then it's release which is faulty, not the
model.

if it does make sense (I'm a bit at a loss when that might be the case,
maybe the "color" is just a code word, or maybe they are colors in a
design which are arbitrary but must be consistent), then the experience
that the user has is exactly the same as if the maintenance release was
applied just after they selected the color. Which might be a bit
confusing but is almost certainly what is wanted.

This is simply saying “what is implemented is certainly wanted, so what’s the point”.

The discussion is about *defining* what is wanted and using DBMS to *enforce* that.

A) Your release changed the sementics of the record 3. It's meaning
changed. I cannot recommend doing that.

If the release changed the semantics of an existing record the release
was almost certainly wrong.

Is it possible to minimize the risk of “wrong releases” using mechanisms that DBMS provides?

B) If you absolutely must change the semantic, put your application
into maintenance mode in which noone can select anything beforehand.

If the maintenance would just correct the typo from GREE to GREEN,
nothing would happen. Yor customer still ordered the lavishly green
E-Bike her hear ever desired.

Yeah, that's a good example where changing the color from GREE to YELLOW
doesn't make sense. Presumably that ID 3 is used as a foreign key in
lots of places, e,g. in an inventory table. Your bikes in stock won't
just magically change color just because you changed some text in the
database. So that change simply doesn't make sense and shouldn't be done
as part of a maintenance release. Confusing a few people who just happen
to open the dropdown in the wrong second is the least of your problems.

We are in agreement here. What I am also saying is:

having color name as PK and all FKs referencing it *prevents* these unwanted updates.

—

Michal