Extend plsample example to include a trigger handler.

tglsfdc · tglsfdc · commit 2f4d0d67994b · 2022-04-07T18:26:20.000-04:00
Mark Wong and Konstantina Skovola, reviewed by Chapman Flack Discussion: https://postgr.es/m/Yd8Cz22eHi80XS30@workstation-mark-wong
diff --git a/src/test/modules/plsample/expected/plsample.out b/src/test/modules/plsample/expected/plsample.out
@@ -34,3 +34,84 @@ NOTICE:  argument: 0; name: a1; value: {foo,bar,hoge}
  
 (1 row)
 
+CREATE FUNCTION my_trigger_func() RETURNS trigger AS $$
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+$$ language plsample;
+CREATE TABLE my_table (num integer, description text);
+CREATE TRIGGER my_trigger_func BEFORE INSERT OR UPDATE ON my_table
+       FOR EACH ROW EXECUTE FUNCTION my_trigger_func();
+CREATE TRIGGER my_trigger_func2 AFTER INSERT OR UPDATE ON my_table
+       FOR EACH ROW EXECUTE FUNCTION my_trigger_func(8);
+INSERT INTO my_table (num, description)
+VALUES (1, 'first');
+NOTICE:  source text of function "my_trigger_func": 
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+
+NOTICE:  trigger name: my_trigger_func
+NOTICE:  trigger relation: my_table
+NOTICE:  trigger relation schema: public
+NOTICE:  triggered by INSERT
+NOTICE:  triggered BEFORE
+NOTICE:  triggered per row
+NOTICE:  source text of function "my_trigger_func": 
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+
+NOTICE:  trigger name: my_trigger_func2
+NOTICE:  trigger relation: my_table
+NOTICE:  trigger relation schema: public
+NOTICE:  triggered by INSERT
+NOTICE:  triggered AFTER
+NOTICE:  triggered per row
+NOTICE:  trigger arg[0]: 8
+UPDATE my_table
+SET description = 'first, modified once'
+WHERE num = 1;
+NOTICE:  source text of function "my_trigger_func": 
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+
+NOTICE:  trigger name: my_trigger_func
+NOTICE:  trigger relation: my_table
+NOTICE:  trigger relation schema: public
+NOTICE:  triggered by UPDATE
+NOTICE:  triggered BEFORE
+NOTICE:  triggered per row
+NOTICE:  source text of function "my_trigger_func": 
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+
+NOTICE:  trigger name: my_trigger_func2
+NOTICE:  trigger relation: my_table
+NOTICE:  trigger relation schema: public
+NOTICE:  triggered by UPDATE
+NOTICE:  triggered AFTER
+NOTICE:  triggered per row
+NOTICE:  trigger arg[0]: 8
diff --git a/src/test/modules/plsample/plsample.c b/src/test/modules/plsample/plsample.c
@@ -19,6 +19,7 @@
 #include "catalog/pg_type.h"
 #include "commands/event_trigger.h"
 #include "commands/trigger.h"
+#include "executor/spi.h"
 #include "funcapi.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
@@ -29,6 +30,7 @@ PG_MODULE_MAGIC;
 PG_FUNCTION_INFO_V1(plsample_call_handler);
 
 static Datum plsample_func_handler(PG_FUNCTION_ARGS);
+static HeapTuple plsample_trigger_handler(PG_FUNCTION_ARGS);
 
 /*
  * Handle function, procedure, and trigger calls.
@@ -38,6 +40,11 @@ plsample_call_handler(PG_FUNCTION_ARGS)
 {
 	Datum		retval = (Datum) 0;
 
+	/*
+	 * Many languages will require cleanup that happens even in the event of
+	 * an error.  That can happen in the PG_FINALLY block.  If none is needed,
+	 * this PG_TRY construct can be omitted.
+	 */
 	PG_TRY();
 	{
 		/*
@@ -51,13 +58,16 @@ plsample_call_handler(PG_FUNCTION_ARGS)
 			 * (TriggerData *) fcinfo->context includes the information of the
 			 * context.
 			 */
+			retval = PointerGetDatum(plsample_trigger_handler(fcinfo));
 		}
 		else if (CALLED_AS_EVENT_TRIGGER(fcinfo))
 		{
 			/*
 			 * This function is called as an event trigger function, where
 			 * (EventTriggerData *) fcinfo->context includes the information
 			 * of the context.
+			 *
+			 * TODO: provide an example handler.
 			 */
 		}
 		else
@@ -101,9 +111,9 @@ plsample_func_handler(PG_FUNCTION_ARGS)
 	FmgrInfo	result_in_func;
 	int			numargs;
 
-	/* Fetch the source text of the function. */
-	pl_tuple = SearchSysCache(PROCOID,
-							  ObjectIdGetDatum(fcinfo->flinfo->fn_oid), 0, 0, 0);
+	/* Fetch the function's pg_proc entry. */
+	pl_tuple = SearchSysCache1(PROCOID,
+							   ObjectIdGetDatum(fcinfo->flinfo->fn_oid));
 	if (!HeapTupleIsValid(pl_tuple))
 		elog(ERROR, "cache lookup failed for function %u",
 			 fcinfo->flinfo->fn_oid);
@@ -185,3 +195,160 @@ plsample_func_handler(PG_FUNCTION_ARGS)
 	ret = InputFunctionCall(&result_in_func, source, result_typioparam, -1);
 	PG_RETURN_DATUM(ret);
 }
+
+/*
+ * plsample_trigger_handler
+ *
+ * Function called by the call handler for trigger execution.
+ */
+static HeapTuple
+plsample_trigger_handler(PG_FUNCTION_ARGS)
+{
+	TriggerData *trigdata = (TriggerData *) fcinfo->context;
+	char	   *string;
+	volatile HeapTuple rettup;
+	HeapTuple	pl_tuple;
+	Datum		ret;
+	char	   *source;
+	bool		isnull;
+	Form_pg_proc pl_struct;
+	char	   *proname;
+	int			rc PG_USED_FOR_ASSERTS_ONLY;
+
+	/* Make sure this is being called from a trigger. */
+	if (!CALLED_AS_TRIGGER(fcinfo))
+		elog(ERROR, "not called by trigger manager");
+
+	/* Connect to the SPI manager */
+	if (SPI_connect() != SPI_OK_CONNECT)
+		elog(ERROR, "could not connect to SPI manager");
+
+	rc = SPI_register_trigger_data(trigdata);
+	Assert(rc >= 0);
+
+	/* Fetch the function's pg_proc entry. */
+	pl_tuple = SearchSysCache1(PROCOID,
+							   ObjectIdGetDatum(fcinfo->flinfo->fn_oid));
+	if (!HeapTupleIsValid(pl_tuple))
+		elog(ERROR, "cache lookup failed for function %u",
+			 fcinfo->flinfo->fn_oid);
+
+	/*
+	 * Code Retrieval
+	 *
+	 * Extract and print the source text of the function.  This can be used as
+	 * a base for the function validation and execution.
+	 */
+	pl_struct = (Form_pg_proc) GETSTRUCT(pl_tuple);
+	proname = pstrdup(NameStr(pl_struct->proname));
+	ret = SysCacheGetAttr(PROCOID, pl_tuple, Anum_pg_proc_prosrc, &isnull);
+	if (isnull)
+		elog(ERROR, "could not find source text of function \"%s\"",
+			 proname);
+	source = DatumGetCString(DirectFunctionCall1(textout, ret));
+	ereport(NOTICE,
+			(errmsg("source text of function \"%s\": %s",
+					proname, source)));
+
+	/*
+	 * We're done with the pg_proc tuple, so release it.  (Note that the
+	 * "proname" and "source" strings are now standalone copies.)
+	 */
+	ReleaseSysCache(pl_tuple);
+
+	/*
+	 * Code Augmentation
+	 *
+	 * The source text may be augmented here, such as by wrapping it as the
+	 * body of a function in the target language, prefixing a parameter list
+	 * with names like TD_name, TD_relid, TD_table_name, TD_table_schema,
+	 * TD_event, TD_when, TD_level, TD_NEW, TD_OLD, and args, using whatever
+	 * types in the target language are convenient. The augmented text can be
+	 * cached in a longer-lived memory context, or, if the target language
+	 * uses a compilation step, that can be done here, caching the result of
+	 * the compilation.
+	 */
+
+	/*
+	 * Code Execution
+	 *
+	 * Here the function (the possibly-augmented source text, or the result of
+	 * compilation if the target language uses such a step) should be
+	 * executed, after binding values from the TriggerData struct to the
+	 * appropriate parameters.
+	 *
+	 * In this example we just print a lot of info via ereport.
+	 */
+
+	PG_TRY();
+	{
+		ereport(NOTICE,
+				(errmsg("trigger name: %s", trigdata->tg_trigger->tgname)));
+		string = SPI_getrelname(trigdata->tg_relation);
+		ereport(NOTICE, (errmsg("trigger relation: %s", string)));
+
+		string = SPI_getnspname(trigdata->tg_relation);
+		ereport(NOTICE, (errmsg("trigger relation schema: %s", string)));
+
+		/* Example handling of different trigger aspects. */
+
+		if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
+		{
+			ereport(NOTICE, (errmsg("triggered by INSERT")));
+			rettup = trigdata->tg_trigtuple;
+		}
+		else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
+		{
+			ereport(NOTICE, (errmsg("triggered by DELETE")));
+			rettup = trigdata->tg_trigtuple;
+		}
+		else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
+		{
+			ereport(NOTICE, (errmsg("triggered by UPDATE")));
+			rettup = trigdata->tg_trigtuple;
+		}
+		else if (TRIGGER_FIRED_BY_TRUNCATE(trigdata->tg_event))
+		{
+			ereport(NOTICE, (errmsg("triggered by TRUNCATE")));
+			rettup = trigdata->tg_trigtuple;
+		}
+		else
+			elog(ERROR, "unrecognized event: %u", trigdata->tg_event);
+
+		if (TRIGGER_FIRED_BEFORE(trigdata->tg_event))
+			ereport(NOTICE, (errmsg("triggered BEFORE")));
+		else if (TRIGGER_FIRED_AFTER(trigdata->tg_event))
+			ereport(NOTICE, (errmsg("triggered AFTER")));
+		else if (TRIGGER_FIRED_INSTEAD(trigdata->tg_event))
+			ereport(NOTICE, (errmsg("triggered INSTEAD OF")));
+		else
+			elog(ERROR, "unrecognized when: %u", trigdata->tg_event);
+
+		if (TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
+			ereport(NOTICE, (errmsg("triggered per row")));
+		else if (TRIGGER_FIRED_FOR_STATEMENT(trigdata->tg_event))
+			ereport(NOTICE, (errmsg("triggered per statement")));
+		else
+			elog(ERROR, "unrecognized level: %u", trigdata->tg_event);
+
+		/*
+		 * Iterate through all of the trigger arguments, printing each input
+		 * value.
+		 */
+		for (int i = 0; i < trigdata->tg_trigger->tgnargs; i++)
+			ereport(NOTICE,
+					(errmsg("trigger arg[%i]: %s", i,
+							trigdata->tg_trigger->tgargs[i])));
+	}
+	PG_CATCH();
+	{
+		/* Error cleanup code would go here */
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+
+	if (SPI_finish() != SPI_OK_FINISH)
+		elog(ERROR, "SPI_finish() failed");
+
+	return rettup;
+}
diff --git a/src/test/modules/plsample/sql/plsample.sql b/src/test/modules/plsample/sql/plsample.sql
@@ -13,3 +13,26 @@ AS $$
   Example of source with void result.
 $$ LANGUAGE plsample;
 SELECT plsample_result_void('{foo, bar, hoge}');
+
+CREATE FUNCTION my_trigger_func() RETURNS trigger AS $$
+if TD_event == "INSERT"
+    return TD_NEW
+elseif TD_event == "UPDATE"
+    return TD_NEW
+else
+    return "OK"
+end
+$$ language plsample;
+
+CREATE TABLE my_table (num integer, description text);
+CREATE TRIGGER my_trigger_func BEFORE INSERT OR UPDATE ON my_table
+       FOR EACH ROW EXECUTE FUNCTION my_trigger_func();
+CREATE TRIGGER my_trigger_func2 AFTER INSERT OR UPDATE ON my_table
+       FOR EACH ROW EXECUTE FUNCTION my_trigger_func(8);
+
+INSERT INTO my_table (num, description)
+VALUES (1, 'first');
+
+UPDATE my_table
+SET description = 'first, modified once'
+WHERE num = 1;
