Re: Proposal: ON UPDATE REMOVE foreign key action - Mailing list pgsql-hackers

On 10/4/16, Kirill Berezin <enelar@exsul.net> wrote:
> Disclaimer: sorry, i dont understand, should i reply to each of you
> personally, or just answer to channel. Some feedbacks were sended in
> personal, and some include channel copy.

Usually discussions are in the list, therefore you should use "reply
to all" (see [1]).
Exception is when a sender notes "Off the list".

> Thanks for responses, you understand it correctly.
>
> When i said "anybody", i mean inclusive owner himself. For example cookie
> poisoning.
> There is no "another" session, technically. They similar to the server,
> they even can have same IP.
> Yes, we can't prevent it with CSRF cookies, but it is not the point of
> current conversation.
>
> I can make business logic outside table: make extra query.

Good decision. Your case needs exactly what you've just written.

> Im just dont like how it looks from perspective of encapsulation.
> Each table should describe itself, like object in OOP language.
> With SQL constructions or triggers/constraits.

SQL is not OOP. There is no "encapsulation".

> Second part of my use case is data cache.

Hmm. Usage of RDBMS as a cache with an overhead for Isolation and
Durability (from ACID)? Really?
As for me it is a bad idea for most cases.

> When user update
> version(generation), cache should be flushed. As easy example: imagine i am
> fetching currency value. And till end of the day, i am honor current
> course. (Or any other information, that has certain origin checkpoints).
> When i am updating origin state (current day, server version, ip address,
> neural network generation), i am have to invalidate all previous data.

It is a bad example. Companies working with currency exchange rates
always keep their values as historical data.

> Like i am calculating digits of the square root, of some number. The more i
> spend time, the closer my approx value to irrational result. But when
> original value has changed - all previous data does not make sense. I am
> flushing it and starting from digit 1.

Why do you "update" original value instead of deleting old one and
inserting new value?

> This is allegorical examples to my real-world cases. I may try imagine some
> hypothetical situations, when this functionality more welcomed. But, i am
> respect reasons why do not apply this proposal. If my update didn't shift
> the balance, its ok. on update trigger is not such painful.

All your cases (except the exchange rate one) can be done using two
queries: delete original row (which deletes other linked data "ON
DELETE CASCADE") and insert a new one. You don't even have to use
transactions!
If your business logic is so "OOP", you can use stored procedures, but
introducing new grammar specially for concrete task is a bad idea.


Of course at first sight there is a meaningless sequence "ON UPDATE
SET (NULL|DEFAULT)", but the meaning of SET NULL and SET DEFAULT for
both ON UPDATE and ON DELETE is using them for "unlinking" data from
the referenced one. It is similar to "NO ACTION" but explicitly change
them as they are no longer connected to the referenced row (by
referencing column list).

Also your proposal is not consistent: ON UPDATE REMOVE (DELETE?), but
ON DELETE - what? again remove/delete?


[1] https://wiki.postgresql.org/wiki/Mailing_Lists#Using_the_discussion_lists
-- 
Best regards,
Vitaly Burovoy