How about this
ad_proc object_exists {
-id:required
} {
@author Jim Lynch (jim@jam.sessionsnet.org)
@creation-date 2007-01-26
@param id
@return true if object whose id is $id exists
} {
return [db_string test_exists \
"select
1
from
acs_objects
where
object_id = :id" \
-default "0"]}