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Commit48756be

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Improve comments about why SET DEFAULT triggers must recheck for matches.
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 turnoff the RI_FKey_keyequal_upd_fk event filter temporarily?)
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‎src/backend/utils/adt/ri_triggers.c

Lines changed: 20 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -2227,12 +2227,16 @@ RI_FKey_setdefault_del(PG_FUNCTION_ARGS)
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heap_close(fk_rel,RowExclusiveLock);
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/*
2230-
* In the case we delete the row who's key is equal to the default
2231-
* values AND a referencing row in the foreign key table exists,
2232-
* we would just have updated it to the same values. We need to do
2233-
* another lookup now and in case a reference exists, abort the
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* operation. That is already implemented in the NO ACTION
2235-
* trigger.
2230+
* If we just deleted the PK row whose key was equal to the FK
2231+
* columns' default values, and a referencing row exists in the FK
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* table, we would have updated that row to the same values it
2233+
* already had --- and RI_FKey_keyequal_upd_fk would therefore
2234+
* believe no check is necessary. So we need to do another lookup
2235+
* now and in case a reference still exists, abort the operation.
2236+
* That is already implemented in the NO ACTION trigger, so just
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* run it. (This recheck is only needed in the SET DEFAULT case,
2238+
* since CASCADE would remove such rows, while SET NULL is certain
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* to result in rows that satisfy the FK constraint.)
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*/
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RI_FKey_noaction_del(fcinfo);
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@@ -2420,12 +2424,16 @@ RI_FKey_setdefault_upd(PG_FUNCTION_ARGS)
24202424
heap_close(fk_rel,RowExclusiveLock);
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/*
2423-
* In the case we updated the row who's key was equal to the
2424-
* default values AND a referencing row in the foreign key table
2425-
* exists, we would just have updated it to the same values. We
2426-
* need to do another lookup now and in case a reference exists,
2427-
* abort the operation. That is already implemented in the NO
2428-
* ACTION trigger.
2427+
* If we just updated the PK row whose key was equal to the FK
2428+
* columns' default values, and a referencing row exists in the FK
2429+
* table, we would have updated that row to the same values it
2430+
* already had --- and RI_FKey_keyequal_upd_fk would therefore
2431+
* believe no check is necessary. So we need to do another lookup
2432+
* now and in case a reference still exists, abort the operation.
2433+
* That is already implemented in the NO ACTION trigger, so just
2434+
* run it. (This recheck is only needed in the SET DEFAULT case,
2435+
* since CASCADE must change the FK key values, while SET NULL is
2436+
* certain to result in rows that satisfy the FK constraint.)
24292437
*/
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RI_FKey_noaction_upd(fcinfo);
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