Fix some issues in contrib/spi/refint.c.

check_foreign_key incorrectly used a single cache entry for its saved
plans for a 'c' (cascade) trigger, although there are two different
queries to execute depending on whether it fires for an update or a
delete.  This caused the wrong things to be done if both types of
event occur in one session.  (This was indeed visible in the triggers
regression test, but apparently nobody ever questioned it.)  To fix,
add the operation type to the cache key.

Its debug log output failed to distinguish update from delete
events, too.

Also, change the intended trigger usage from BEFORE ROW to AFTER ROW,
and add checks insisting on that usage.  BEFORE is really rather
unsafe, since if there are other BEFORE triggers they might change or
cancel the operation we are trying to check.  AFTER triggers are the
standard way to propagate changes to other rows, so we should follow
that way here.

In passing, remove a useless duplicate lookup of the cache entry.

This code is mostly intended as a documentation example, so we
won't consider a back-patch.

Author: Dmitrii Bondar <[email protected]>
Reviewed-by: Paul Jungwirth <[email protected]>
Reviewed-by: Lilian Ontowhee <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/[email protected]

4 files changed, 55 insertions, 34 deletions

diff --git a/contrib/spi/refint.c b/contrib/spi/refint.c
index d954f5c838f..d5e25e07ae9 100644
--- a/contrib/spi/refint.c
+++ b/contrib/spi/refint.c
@@ -84,6 +84,10 @@ check_primary_key(PG_FUNCTION_ARGS)
 		/* internal error */
 		elog(ERROR, "check_primary_key: must be fired for row");
 
+	if (!TRIGGER_FIRED_AFTER(trigdata->tg_event))
+		/* internal error */
+		elog(ERROR, "check_primary_key: must be fired by AFTER trigger");
+
 	/* If INSERTion then must check Tuple to being inserted */
 	if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
 		tuple = trigdata->tg_trigtuple;
@@ -287,6 +291,10 @@ check_foreign_key(PG_FUNCTION_ARGS)
 		/* internal error */
 		elog(ERROR, "check_foreign_key: cannot process INSERT events");
 
+	if (!TRIGGER_FIRED_AFTER(trigdata->tg_event))
+		/* internal error */
+		elog(ERROR, "check_foreign_key: must be fired by AFTER trigger");
+
 	/* Have to check tg_trigtuple - tuple being deleted */
 	trigtuple = trigdata->tg_trigtuple;
 
@@ -338,10 +346,10 @@ check_foreign_key(PG_FUNCTION_ARGS)
 	kvals = (Datum *) palloc(nkeys * sizeof(Datum));
 
 	/*
-	 * Construct ident string as TriggerName $ TriggeredRelationId and try to
-	 * find prepared execution plan(s).
+	 * Construct ident string as TriggerName $ TriggeredRelationId $
+	 * OperationType and try to find prepared execution plan(s).
 	 */
-	snprintf(ident, sizeof(ident), "%s$%u", trigger->tgname, rel->rd_id);
+	snprintf(ident, sizeof(ident), "%s$%u$%c", trigger->tgname, rel->rd_id, is_update ? 'U' : 'D');
 	plan = find_plan(ident, &FPlans, &nFPlans);
 
 	/* if there is no plan(s) then allocate argtypes for preparation */
@@ -573,8 +581,6 @@ check_foreign_key(PG_FUNCTION_ARGS)
 
 		relname = args[0];
 
-		snprintf(ident, sizeof(ident), "%s$%u", trigger->tgname, rel->rd_id);
-		plan = find_plan(ident, &FPlans, &nFPlans);
 		ret = SPI_execp(plan->splan[r], kvals, NULL, tcount);
 		/* we have no NULLs - so we pass   ^^^^  here */
 
@@ -596,9 +602,15 @@ check_foreign_key(PG_FUNCTION_ARGS)
 		else
 		{
 #ifdef REFINT_VERBOSE
+			const char *operation;
+
+			if (action == 'c')
+				operation = is_update ? "updated" : "deleted";
+			else
+				operation = "set to null";
+
 			elog(NOTICE, "%s: " UINT64_FORMAT " tuple(s) of %s are %s",
-				 trigger->tgname, SPI_processed, relname,
-				 (action == 'c') ? "deleted" : "set to null");
+				 trigger->tgname, SPI_processed, relname, operation);
 #endif
 		}
 		args += nkeys + 1;		/* to the next relation */
diff --git a/doc/src/sgml/contrib-spi.sgml b/doc/src/sgml/contrib-spi.sgml
index e7cae4e38dc..55d3fac7a69 100644
--- a/doc/src/sgml/contrib-spi.sgml
+++ b/doc/src/sgml/contrib-spi.sgml
@@ -36,7 +36,7 @@
 
   <para>
    <function>check_primary_key()</function> checks the referencing table.
-   To use, create a <literal>BEFORE INSERT OR UPDATE</literal> trigger using this
+   To use, create an <literal>AFTER INSERT OR UPDATE</literal> trigger using this
    function on a table referencing another table. Specify as the trigger
    arguments: the referencing table's column name(s) which form the foreign
    key, the referenced table name, and the column names in the referenced table
@@ -46,7 +46,7 @@
 
   <para>
    <function>check_foreign_key()</function> checks the referenced table.
-   To use, create a <literal>BEFORE DELETE OR UPDATE</literal> trigger using this
+   To use, create an <literal>AFTER DELETE OR UPDATE</literal> trigger using this
    function on a table referenced by other table(s).  Specify as the trigger
    arguments: the number of referencing tables for which the function has to
    perform checking, the action if a referencing key is found
@@ -61,6 +61,16 @@
   </para>
 
   <para>
+   Note that if these triggers are executed from
+   another <literal>BEFORE</literal> trigger, they can fail unexpectedly. For
+   example, if a user inserts row1 and then the <literal>BEFORE</literal>
+   trigger inserts row2 and calls a trigger with the
+   <function>check_foreign_key()</function>,
+   the <function>check_foreign_key()</function>
+   function will not see row1 and will fail.
+  </para>
+
+  <para>
    There are examples in <filename>refint.example</filename>.
   </para>
  </sect2>
diff --git a/src/test/regress/expected/triggers.out b/src/test/regress/expected/triggers.out
index 247c67c32ae..e6f585d9740 100644
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -46,12 +46,12 @@ create unique index pkeys_i on pkeys (pkey1, pkey2);
 -- 	(fkey3)		--> fkeys2 (pkey23)
 --
 create trigger check_fkeys_pkey_exist
-	before insert or update on fkeys
+	after insert or update on fkeys
 	for each row
 	execute function
 	check_primary_key ('fkey1', 'fkey2', 'pkeys', 'pkey1', 'pkey2');
 create trigger check_fkeys_pkey2_exist
-	before insert or update on fkeys
+	after insert or update on fkeys
 	for each row
 	execute function check_primary_key ('fkey3', 'fkeys2', 'pkey23');
 --
@@ -59,7 +59,7 @@ create trigger check_fkeys_pkey2_exist
 -- 	(fkey21, fkey22)	--> pkeys (pkey1, pkey2)
 --
 create trigger check_fkeys2_pkey_exist
-	before insert or update on fkeys2
+	after insert or update on fkeys2
 	for each row
 	execute procedure
 	check_primary_key ('fkey21', 'fkey22', 'pkeys', 'pkey1', 'pkey2');
@@ -74,7 +74,7 @@ COMMENT ON TRIGGER check_fkeys2_pkey_exist ON fkeys2 IS NULL;
 -- 		fkeys (fkey1, fkey2) and fkeys2 (fkey21, fkey22)
 --
 create trigger check_pkeys_fkey_cascade
-	before delete or update on pkeys
+	after delete or update on pkeys
 	for each row
 	execute procedure
 	check_foreign_key (2, 'cascade', 'pkey1', 'pkey2',
@@ -85,7 +85,7 @@ create trigger check_pkeys_fkey_cascade
 -- 		fkeys (fkey3)
 --
 create trigger check_fkeys2_fkey_restrict
-	before delete or update on fkeys2
+	after delete or update on fkeys2
 	for each row
 	execute procedure check_foreign_key (1, 'restrict', 'pkey23', 'fkeys', 'fkey3');
 insert into fkeys2 values (10, '1', 1);
@@ -116,12 +116,11 @@ delete from pkeys where pkey1 = 40 and pkey2 = '4';
 NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys are deleted
 NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys2 are deleted
 update pkeys set pkey1 = 7, pkey2 = '70' where pkey1 = 50 and pkey2 = '5';
-NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys are deleted
-ERROR:  "check_fkeys2_fkey_restrict": tuple is referenced in "fkeys"
-CONTEXT:  SQL statement "delete from fkeys2 where fkey21 = $1 and fkey22 = $2 "
+NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys are updated
+NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys2 are updated
 update pkeys set pkey1 = 7, pkey2 = '70' where pkey1 = 10 and pkey2 = '1';
-NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys are deleted
-NOTICE:  check_pkeys_fkey_cascade: 1 tuple(s) of fkeys2 are deleted
+ERROR:  duplicate key value violates unique constraint "pkeys_i"
+DETAIL:  Key (pkey1, pkey2)=(7, 70) already exists.
 SELECT trigger_name, event_manipulation, event_object_schema, event_object_table,
        action_order, action_condition, action_orientation, action_timing,
        action_reference_old_table, action_reference_new_table
@@ -130,16 +129,16 @@ SELECT trigger_name, event_manipulation, event_object_schema, event_object_table
   ORDER BY trigger_name COLLATE "C", 2;
         trigger_name        | event_manipulation | event_object_schema | event_object_table | action_order | action_condition | action_orientation | action_timing | action_reference_old_table | action_reference_new_table 
 ----------------------------+--------------------+---------------------+--------------------+--------------+------------------+--------------------+---------------+----------------------------+----------------------------
- check_fkeys2_fkey_restrict | DELETE             | public              | fkeys2             |            1 |                  | ROW                | BEFORE        |                            | 
- check_fkeys2_fkey_restrict | UPDATE             | public              | fkeys2             |            1 |                  | ROW                | BEFORE        |                            | 
- check_fkeys2_pkey_exist    | INSERT             | public              | fkeys2             |            1 |                  | ROW                | BEFORE        |                            | 
- check_fkeys2_pkey_exist    | UPDATE             | public              | fkeys2             |            2 |                  | ROW                | BEFORE        |                            | 
- check_fkeys_pkey2_exist    | INSERT             | public              | fkeys              |            1 |                  | ROW                | BEFORE        |                            | 
- check_fkeys_pkey2_exist    | UPDATE             | public              | fkeys              |            1 |                  | ROW                | BEFORE        |                            | 
- check_fkeys_pkey_exist     | INSERT             | public              | fkeys              |            2 |                  | ROW                | BEFORE        |                            | 
- check_fkeys_pkey_exist     | UPDATE             | public              | fkeys              |            2 |                  | ROW                | BEFORE        |                            | 
- check_pkeys_fkey_cascade   | DELETE             | public              | pkeys              |            1 |                  | ROW                | BEFORE        |                            | 
- check_pkeys_fkey_cascade   | UPDATE             | public              | pkeys              |            1 |                  | ROW                | BEFORE        |                            | 
+ check_fkeys2_fkey_restrict | DELETE             | public              | fkeys2             |            1 |                  | ROW                | AFTER         |                            | 
+ check_fkeys2_fkey_restrict | UPDATE             | public              | fkeys2             |            1 |                  | ROW                | AFTER         |                            | 
+ check_fkeys2_pkey_exist    | INSERT             | public              | fkeys2             |            1 |                  | ROW                | AFTER         |                            | 
+ check_fkeys2_pkey_exist    | UPDATE             | public              | fkeys2             |            2 |                  | ROW                | AFTER         |                            | 
+ check_fkeys_pkey2_exist    | INSERT             | public              | fkeys              |            1 |                  | ROW                | AFTER         |                            | 
+ check_fkeys_pkey2_exist    | UPDATE             | public              | fkeys              |            1 |                  | ROW                | AFTER         |                            | 
+ check_fkeys_pkey_exist     | INSERT             | public              | fkeys              |            2 |                  | ROW                | AFTER         |                            | 
+ check_fkeys_pkey_exist     | UPDATE             | public              | fkeys              |            2 |                  | ROW                | AFTER         |                            | 
+ check_pkeys_fkey_cascade   | DELETE             | public              | pkeys              |            1 |                  | ROW                | AFTER         |                            | 
+ check_pkeys_fkey_cascade   | UPDATE             | public              | pkeys              |            1 |                  | ROW                | AFTER         |                            | 
 (10 rows)
 
 DROP TABLE pkeys;
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index 659972f1135..e5a491be7ab 100644
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -57,13 +57,13 @@ create unique index pkeys_i on pkeys (pkey1, pkey2);
 -- 	(fkey3)		--> fkeys2 (pkey23)
 --
 create trigger check_fkeys_pkey_exist
-	before insert or update on fkeys
+	after insert or update on fkeys
 	for each row
 	execute function
 	check_primary_key ('fkey1', 'fkey2', 'pkeys', 'pkey1', 'pkey2');
 
 create trigger check_fkeys_pkey2_exist
-	before insert or update on fkeys
+	after insert or update on fkeys
 	for each row
 	execute function check_primary_key ('fkey3', 'fkeys2', 'pkey23');
 
@@ -72,7 +72,7 @@ create trigger check_fkeys_pkey2_exist
 -- 	(fkey21, fkey22)	--> pkeys (pkey1, pkey2)
 --
 create trigger check_fkeys2_pkey_exist
-	before insert or update on fkeys2
+	after insert or update on fkeys2
 	for each row
 	execute procedure
 	check_primary_key ('fkey21', 'fkey22', 'pkeys', 'pkey1', 'pkey2');
@@ -88,7 +88,7 @@ COMMENT ON TRIGGER check_fkeys2_pkey_exist ON fkeys2 IS NULL;
 -- 		fkeys (fkey1, fkey2) and fkeys2 (fkey21, fkey22)
 --
 create trigger check_pkeys_fkey_cascade
-	before delete or update on pkeys
+	after delete or update on pkeys
 	for each row
 	execute procedure
 	check_foreign_key (2, 'cascade', 'pkey1', 'pkey2',
@@ -100,7 +100,7 @@ create trigger check_pkeys_fkey_cascade
 -- 		fkeys (fkey3)
 --
 create trigger check_fkeys2_fkey_restrict
-	before delete or update on fkeys2
+	after delete or update on fkeys2
 	for each row
 	execute procedure check_foreign_key (1, 'restrict', 'pkey23', 'fkeys', 'fkey3');