Index: openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.0.0a5-5.0.0a6.sql
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.0.0a5-5.0.0a6.sql,v
diff -u -r1.1.2.3 -r1.1.2.4
--- openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.0.0a5-5.0.0a6.sql	2 Dec 2003 10:45:27 -0000	1.1.2.3
+++ openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.0.0a5-5.0.0a6.sql	4 Feb 2004 10:57:13 -0000	1.1.2.4
@@ -1,15 +1,43 @@
 -- Add on delete cascade to the notifications.response_id column foreign key constraint
 -- see Bug http://openacs.org/bugtracker/openacs/bug?filter%2estatus=resolved&filter%2eactionby=6815&bug%5fnumber=260
 -- @author Peter Marklund
-alter table notifications drop constraint notif_reponse_id_fk;
+
+create or replace function safe_drop_cosntraint(name, name)
+returns integer as '
+declare
+    p_table_name          alias for $1;
+    p_constraint_name     alias for $2;
+    v_constraint_p        integer;
+begin
+    select count(*)
+    into   v_constraint_p
+    from   pg_constraint con, pg_class c
+    where  con.conname = p_constraint_name
+    and    c.oid = con.conrelid
+    and    c.relname = p_table_name;
+
+    if v_constraint_p > 0 then
+        execute ''alter table '' || p_table_name || '' drop constraint '' || p_constraint_name;
+    end if;
+
+    return 0;
+end;' language 'plpgsql';
+
+select safe_drop_cosntraint('notifications', 'notif_reponse_id_fk');
+
 alter table notifications add constraint notif_reponse_id_fk
                               foreign key (response_id)
                               references acs_objects (object_id)
                               on delete cascade;
 
 -- Add on delete cascade to notification_user_map.notification_in foreign key constraint
-alter table notification_user_map drop constraint notif_user_map_notif_id_fk;
+
+select safe_drop_cosntraint('notification_user_map', 'notif_user_map_notif_id_fk');
+
 alter table notification_user_map add constraint notif_user_map_notif_id_fk 
                                       foreign key (notification_id) 
                                       references notifications(notification_id) 
                                       on delete cascade;
+
+drop function safe_drop_cosntraint(name, name);
+