Re: Foreign Key Constraint Deletion Order

Thanks! Stephan,

> We've been having discussions on hackers about the
behavior,
> but it's unlikely that the rows will be deleted
before
> the master row.

Then I am in big big trouble! Please imagine a very
usual scenario:

create table PurchaseMaster (book text primary key,
UnitPrice float);

create table PurchaseDetail (
CONSTRAINT fk_abc FOREIGN KEY (book) REFERENCES
PurchaseMaster (book) on delete cascade on update
cascade,
primary key (book,buyer),
book text,
buyer text,
quantity smallint
);

create table HowMuchIOwe (buyer text primary
key,amount float);

CREATE FUNCTION MyTrigger() RETURNS opaque AS '
BEGIN
UPDATE HowMuchIOwe set
amount=amount-old.quantity*(select UnitPrice from
PurchaseMaster where book=old.book)
where buyer=old.buyer;
END;

CREATE TRIGGER TriggerDetail AFTER DELETE ON
PurchaseDetail FOR EACH ROW EXECUTE PROCEDURE
MyTrigger(
);

Now when a row in PurchaseMaster is deleted by user,
because:

(1) getting rid of fk_abc constraint and replacing it
with a custom trigger function associated with
PurchaseMaster in order to delete PurchaseDetail
"manually" does not work either since PurchaseMaster
row may be deleted BEFORE this custom trigger
function is called;

(2) and row in PurchaseMaster may be deleted before
PurchaseDetail.

so I have no way out!

CN

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