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Improve comments about why SET DEFAULT triggers must recheck for matches.

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I was confused about this, so try to make it clearer for the next person.

(This seems like a fairly inefficient way of dealing with a corner case,
but I don't have a better idea offhand.  Maybe if there were a way to turn
off the RI_FKey_keyequal_upd_fk event filter temporarily?)
This commit is contained in:
Tom Lane
2012-06-18 22:45:07 -04:00
parent e8c9fd5fdf
commit 48756be9cf
1 changed files with 20 additions and 12 deletions
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32
src/backend/utils/adt/ri_triggers.c
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@ -2227,12 +2227,16 @@ RI_FKey_setdefault_del(PG_FUNCTION_ARGS)
heap_close(fk_rel, RowExclusiveLock); heap_close(fk_rel, RowExclusiveLock);
/* /*
* In the case we delete the row who's key is equal to the default * If we just deleted the PK row whose key was equal to the FK
* values AND a referencing row in the foreign key table exists, * columns' default values, and a referencing row exists in the FK
* we would just have updated it to the same values. We need to do * table, we would have updated that row to the same values it
* another lookup now and in case a reference exists, abort the * already had --- and RI_FKey_keyequal_upd_fk would therefore
* operation. That is already implemented in the NO ACTION * believe no check is necessary. So we need to do another lookup
* trigger. * now and in case a reference still exists, abort the operation.
* That is already implemented in the NO ACTION trigger, so just
* run it. (This recheck is only needed in the SET DEFAULT case,
* since CASCADE would remove such rows, while SET NULL is certain
* to result in rows that satisfy the FK constraint.)
*/ */
RI_FKey_noaction_del(fcinfo); RI_FKey_noaction_del(fcinfo);
@ -2420,12 +2424,16 @@ RI_FKey_setdefault_upd(PG_FUNCTION_ARGS)
heap_close(fk_rel, RowExclusiveLock); heap_close(fk_rel, RowExclusiveLock);
/* /*
* In the case we updated the row who's key was equal to the * If we just updated the PK row whose key was equal to the FK
* default values AND a referencing row in the foreign key table * columns' default values, and a referencing row exists in the FK
* exists, we would just have updated it to the same values. We * table, we would have updated that row to the same values it
* need to do another lookup now and in case a reference exists, * already had --- and RI_FKey_keyequal_upd_fk would therefore
* abort the operation. That is already implemented in the NO * believe no check is necessary. So we need to do another lookup
* ACTION trigger. * now and in case a reference still exists, abort the operation.
* That is already implemented in the NO ACTION trigger, so just
* run it. (This recheck is only needed in the SET DEFAULT case,
* since CASCADE must change the FK key values, while SET NULL is
* certain to result in rows that satisfy the FK constraint.)
*/ */
RI_FKey_noaction_upd(fcinfo); RI_FKey_noaction_upd(fcinfo);