On 10 Nov 2001 at 20:41 (-0500), Tom Lane wrote:
| Brent Verner <brent@rcfile.org> writes:
| > ... but we have to check both PK_RELNAME and FK_RELNAME,
| > since we don't know which side of the constraint this relname is on.
|
| But we do, because we know whether we're scanning by tgrelid or
| tgconstrrelid.
My brain is not stretching far enough to see this. Yes, we know
what we are scanning on, but that stilll doesn't tell us which
side of the FK/PK relation this relname is on.
CREATE TABLE p_rel (id int UNIQUE);
CREATE TABLE f_rel (id int REFERENCES p_rel(id) ON UPDATE CASCADE);
p_rel.id is our PK
f_rel.id is our FK
scan on tgrelid==p_rel.oid : 2 tuples.
scan on tgconstrrelid==p_rel.oid : 1 tuple.
scan on tgrelid==f_rel.oid : 1 tuple.
scan on tgconstrrelid==f_rel.oid : 2 tuples.
AFAICS, given a relname, the only way we can know if it is the PK or
FK is the number of tuples a known scan returns. What am I missing
here?
| Another thing in the back of my mind is that I think ALTER RENAME TABLE
| has the same problem as ALTER RENAME COLUMN: the relnames in RI triggers
| need to be fixed, and aren't getting fixed. It seems to me that this
| scan subroutine could be the workhorse for solving both problems, if
| it's defined to do string substitution in a particular field of the
| RI trigger args. The scan subr should be something like
|
| update_ri_trigger_args (Oid relid,
| bool scan_by_constrrelid,
| int tgargs_item_num,
| const char *oldname,
| const char *newname)
I wasn't aware of the related ALTER RENAME TABLE problem. This is
certainly an appropriate solution. I'll work to do what you suggest.
| BTW, you probably need a CommandCounterIncrement between the two scans
| in each case. Otherwise the second scan doesn't see the tuples already
| updated by the first, which is deadly if there are any self-referential
| triggers.
cool. Thanks for alerting me of this danger -- I had no idea.
thanks.
b
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