User based permission on a table

Hello,

I have the following problem. I have a database with different tables.
This database is accessed from different users using different logins to
access some of the tables.
It's not a problem to limit the access of these users to certain tables.
They can be included into a group and allowed access based on group
granting to tables.

My problem is to set these users to be able to access (SELECT| MODIFY|
UPDATE) some rows
from a given table based on some information from the given row.

For example:
We have various locations (discos) where people are visitors. These
locations store the visitors into a table.

Table:

CREATE TABLE "visitors" (
"visitor_id" SERIAL,
"login" text,
"password" text,
"disco_id" int4
);

Each disco (location) is accessing the database with their own login (ie:
disco1, disco2).
Each disco has a disco_id. It is linked to the login which the disco uses
to access the database.
For one login more than one disco_id can be assigned, so with a given login
several disco_id accesses are allowed.

For this I set up a permission table where we have:

create table permissions (
disco_id int4,
username name not null
);
here we have for example:
35 disco1
40 disco1
44 disco2

Users logged in with "disco1" should be able to INSERT, SELECT, MODIFY data
from the visitors table where the disco_id is 35 or 40 in our example.

Let's hide the visitors table from there users and let them think that we
use besucher table to store these visitors data.

For this I define a view:

create view besucher as
select v.* from visitors v, permissions P
where v.disco_id=P.disco_id
AND P.username = CURRENT_USER;

So if I log in as user "disco1" and enter:
select * from besucher; then I get only user from
disco 35 and 40.

This is good. SELECT IS SOLVED.

Now if I set a RULE like:

create rule visitors_del as ON DELETE TO besucher
DO INSTEAD DELETE FROM visitors WHERE
visitor_id=OLD.visitor_id
AND permissions.username = CURRENT_USER
AND visitors.disco_id=permissions.disco_id;

This allows me to not to be able to delete just the visitors belonging
to disco 35 and 40.

So:
delete from visitors; - would only delete the users belonging to disco
35, 40. So far this is ok aswell.

The problem is that I can't create rules for insert and update.
For insert I wanted to set up something like:

create rule visitors_ins as ON INSERT TO besucher
WHERE NEW.disco_id!=permissions.disco_id
AND permissions.username = CURRENT_USER
DO INSTEAD NOTHING;

So if I want to insert a row where disco_id is not available in the
permissions table to the current user - just skip it, do nothing.
Unfortunately this rule cannot be created the way I wrote above.

Can anybody tell me how this can be realized or to give some better
solutions ideas?

The ideea is, to not to allow users who logged in with user "disco1" for
example to access
data othen than they are allowed to access in the permissions table.

Hope someone around is able to inspire me. :)

l8r

Andreas Rust - webnova GmbH
rust(at)webnova(dot)de - www.webnova.de
Tel: +49 (0)234 - 912 96 10
Fax: +49 (0)234 - 912 96 15
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