sub query constraint
I am trying to develop a database table column that is contrainted to a
subset of another table column. I have tried using foreign key, check,
and inheritance, but I cannot figure out how to do it. I have a
user_data table that has various user columns including name and the
bool column write_access. I have another table to record user actions
and this table needs to have a user column whose value can only be one
of "SELECT name from user_data where write_access = 't'". Any
suggestions about how I could accomplish this? I asked a similar
question in the past and Qingqing mentioned pg DOMAINS, but this does
not really fit with what I want to do. I could seperate my users into 2
or more tables "write_access, read_only, other" but I would rather keep
all user data in the same place.
CREATE TABLE user_data(
name varchar(32),
write_access bool DEFAULT 'f'
);
CREATE TABLE actions(
action varchar(32),
user varchar(32) -- somehow make sure user = user_data.name where
user_data.write_access = 't'
);
Thanks,
Dale
On Mon, Mar 28, 2005 at 16:13:59 -0600,
Dale Sykora <dalen@czexan.net> wrote:
CREATE TABLE user_data(
name varchar(32),
write_access bool DEFAULT 'f'
);
CREATE TABLE actions(
action varchar(32),
user varchar(32) -- somehow make sure user = user_data.name where
user_data.write_access = 't'
);
One way to do this is to add a write_access column to actions and use
a constraint to force it to be true. Create a UNIQUE key of
(name, write_access) for user_data and then add a FOREIGN KEY
reference from (name, write_access) in actions to (name, write_access)
in user_data.
One way to do this is to add a write_access column to actions and use
a constraint to force it to be true.
Create a UNIQUE key of
(name, write_access) for user_data and then add a FOREIGN KEY
reference from (name, write_access) in actions to (name, write_access)
in user_data.
Yes the name must unique indexed but couldn't force the write_access
to always 'true'.
I may suggest create a trigger function to validate insert to table actions:
CREATE OR REPLACE FUNCTION validate_actions_insert() RETRUNS OPAQUE AS '
DECLARE
rs RECORD;
BEGIN
SELECT INTO rs * FROM user_data WHERE name = NEW.user and write_access = 't';
IF NOT FOUND THEN
RAISE EXCEPTION ''writing access forbidden for user '', NEW.user;
END IF;
RETURN NEW;
END;
' LANGUAGE plpgsql;
CREATE TRIGGER tg_actions BEFORE INSERT OR UPDATE ON actions
FOR EACH ROW EXECUTE PROCEDURE validate_actions_insert();
You may need create another trigger for table user_data before update
for reverse validation.
Yudie Pg wrote:
One way to do this is to add a write_access column to actions and use
a constraint to force it to be true.
Create a UNIQUE key of
(name, write_access) for user_data and then add a FOREIGN KEY
reference from (name, write_access) in actions to (name, write_access)
in user_data.Yes the name must unique indexed but couldn't force the write_access
to always 'true'.
I may suggest create a trigger function to validate insert to table actions:CREATE OR REPLACE FUNCTION validate_actions_insert() RETRUNS OPAQUE AS '
DECLARE
rs RECORD;BEGIN
SELECT INTO rs * FROM user_data WHERE name = NEW.user and write_access = 't';IF NOT FOUND THEN
RAISE EXCEPTION ''writing access forbidden for user '', NEW.user;
END IF;RETURN NEW;
END;
' LANGUAGE plpgsql;CREATE TRIGGER tg_actions BEFORE INSERT OR UPDATE ON actions
FOR EACH ROW EXECUTE PROCEDURE validate_actions_insert();You may need create another trigger for table user_data before update
for reverse validation.
Bruno and Yudie,
Thanks for the replies. I will read up on triggers and give that a try.
Thanks,
Dale
Yudie Pg wrote:
CREATE OR REPLACE FUNCTION validate_actions_insert() RETRUNS OPAQUE AS '
CREATE OR REPLACE FUNCTION validate_actions_insert() RETURNS OPAQUE AS $$
DECLARE
rs RECORD;BEGIN
SELECT INTO rs * FROM user_data WHERE name = NEW.user and write_access = 't';IF NOT FOUND THEN
RAISE EXCEPTION ''writing access forbidden for user '', NEW.user;
RAISE EXCEPTION 'writing access forbidden for user %', NEW.user;
END IF;
RETURN NEW;
END;
' LANGUAGE plpgsql;
$$ LANGUAGE plpgsql;
CREATE TRIGGER tg_actions BEFORE INSERT OR UPDATE ON actions
FOR EACH ROW EXECUTE PROCEDURE validate_actions_insert();
Yugi,
I made a few minor modifications as shown above and the trigger
function works great. I think I'll also use triggers to keep a history
of record changes for auditing.
Thanks,
Dale