CONTRIBDIR=$(LIBDIR)/contrib

autoinc$(DLSUFFIX) autoinc.sql \

insert_username$(DLSUFFIX) insert_username.sql

install:: all $(CONTRIBDIR)

$(INSTALL) -c README $(CONTRIBDIR)/README.spi

for f in *.example *.sql *$(DLSUFFIX); do $(INSTALL) -c $$f $(CONTRIBDIR)/$$f; done

$(CONTRIBDIR):

mkdir -p $(CONTRIBDIR)

sed -e "s:_OBJWD_:$(CONTRIBDIR):g" \

4. insert_username.c - function for inserting user names.

You have to create BEFORE INSERT OR UPDATE trigger using the function

insert_username(). You have to specify as a function argument: the column

name (of text type) in which user names will be inserted. Note that user

names will be inserted irregardless of the initial value of the field, so

that users cannot bypass this functionality by simply defining the field to

be NOT NULL.

There is an example in insert_username.example.

To CREATE FUNCTION use insert_username.sql (will be made by gmake from

insert_username.source).

#include "executor/spi.h" /* this is what you need to work with SPI */

#include "commands/trigger.h" /* -"- and triggers */

#include "miscadmin.h" /* for GetPgUserName() */

HeapTuple insert_username (void);

insert_username ()

{

Trigger *trigger; /* to get trigger name */

int nargs; /* # of arguments */

Datum newval; /* new value of column */

char **args; /* arguments */

char *relname; /* triggered relation name */

Relation rel; /* triggered relation */

HeapTuple rettuple = NULL;

TupleDesc tupdesc; /* tuple description */

int attnum;

/* sanity checks from autoinc.c */

if (!CurrentTriggerData)

elog(WARN, "insert_username: triggers are not initialized");

if (TRIGGER_FIRED_FOR_STATEMENT(CurrentTriggerData->tg_event))

elog(WARN, "insert_username: can't process STATEMENT events");

if (TRIGGER_FIRED_AFTER(CurrentTriggerData->tg_event))

elog(WARN, "insert_username: must be fired before event");

if (TRIGGER_FIRED_BY_INSERT(CurrentTriggerData->tg_event))

rettuple = CurrentTriggerData->tg_trigtuple;

else if (TRIGGER_FIRED_BY_UPDATE(CurrentTriggerData->tg_event))

rettuple = CurrentTriggerData->tg_newtuple;

else

elog(WARN, "insert_username: can't process DELETE events");

rel = CurrentTriggerData->tg_relation;

relname = SPI_getrelname(rel);

trigger = CurrentTriggerData->tg_trigger;

nargs = trigger->tgnargs;

if (nargs != 1)

elog(WARN, "insert_username (%s): one argument was expected", relname);

args = trigger->tgargs;

tupdesc = rel->rd_att;

CurrentTriggerData = NULL;

attnum = SPI_fnumber (tupdesc, args[0]);

if ( attnum < 0 )

elog(WARN, "insert_username (%s): there is no attribute %s", relname, args[0]);

if (SPI_gettypeid (tupdesc, attnum) != TEXTOID)

elog(WARN, "insert_username (%s): attribute %s must be of TEXT type",

relname, args[0]);

/* create fields containing name */

newval = PointerGetDatum (textin (GetPgUserName ()));

/* construct new tuple */

rettuple = SPI_modifytuple (rel, rettuple, 1, &attnum, &newval, NULL);

if ( rettuple == NULL )

elog (WARN, "insert_username (%s): %d returned by SPI_modifytuple",

relname, SPI_result);

pfree (relname);

return (rettuple);

}

DROP TABLE username_test;

CREATE TABLE username_test (

name text,

username text not null

);

CREATE TRIGGER insert_usernames

BEFORE INSERT OR UPDATE ON username_test

FOR EACH ROW

EXECUTE PROCEDURE insert_username (username);

INSERT INTO username_test VALUES ('nothing');

INSERT INTO username_test VALUES ('null', null);

INSERT INTO username_test VALUES ('empty string', '');

INSERT INTO username_test VALUES ('space', ' ');

INSERT INTO username_test VALUES ('tab', ' ');

INSERT INTO username_test VALUES ('name', 'name');

SELECT * FROM username_test;

DROP FUNCTION insert_username();

CREATE FUNCTION insert_username()

RETURNS opaque

AS '_OBJWD_/insert_username_DLSUFFIX_'

LANGUAGE 'c';