Re: protected ON DELETE CASCADE

i neglected to show it properly

have tables A, B, C, D PLUS a few others

A <- B

F
|
v
A <- C <- D
^
|
E

i want to delete from C and cascade any delete to E or F but not if
there are records in D

what i have done is to have ON DELETE CASCADE on C's primary

but force deletes to C through a function that will delete from C only
if there is no records in D

but i would like to believe there is a better way - a way that does not
require that i do all my deletes through a function

cheers

murray

Oliver Elphick wrote:
>
> Murray Hobbs wrote:
> >
> >here's my problem
> >
> >i have tables A, B, C, D
> >
> >A <- B
> >A <- C <- D
> >
> >i want to maintain integrity so that if A is deleted from then so is
> >anything referencing from B and C - no problem ON DELETE CASCADE
> >
> >but if there are any D's that point back to A (through composite key in
> >C) i don't want the delete to go ahead - at all - i want an error
> >message and condition
>
> If the reference from D to C uses ON DELETE RESTRICT (or NO ACTION), that
> should fail and thus cause the original DELETE to fail.
>
> --
> Oliver Elphick Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
> Isle of Wight http://www.lfix.co.uk/oliver
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> salvation by our Lord Jesus Christ, Who died for us,
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> together with him."
> I Thessalonians 5:9,10

Jan Wieck wrote:
>
> Murray Hobbs wrote:
> >
> > here's my problem
> >
> > i have tables A, B, C, D
> >
> > A <- B
> > A <- C <- D
> >
> > i want to maintain integrity so that if A is deleted from then so is
> > anything referencing from B and C - no problem ON DELETE CASCADE
> >
> > but if there are any D's that point back to A (through composite key in
> > C) i don't want the delete to go ahead - at all - i want an error
> > message and condition
>
> So B and C reference A with ON DELETE CASCADE, while D
> references C without it. The default behaviour of a foreign
> key constraint is ON DELETE NO ACTION, which confusingly
> enough aborts the transaction (it's defined that way in the
> SQL standard, don't ask me why they called it NO ACTION).
> Thus a deletion from A will cascaded delete from C, but then
> the constraint on D will abort the transaction if this
> automatic delete from C would orphan a reference from D.
>
> Jan
>
> --
>
> #======================================================================#
> # It's easier to get forgiveness for being wrong than for being right. #
> # Let's break this rule - forgive me. #
> #================================================== JanWieck(at)Yahoo(dot)com #
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