Re: Rules, Triggers something more challenging

> -----Original Message-----
> From: Peter Csaba [mailto:cpeter(at)webnova(dot)ro]
> Sent: Thursday, April 03, 2003 1:18 PM
> To: Tamir Halperin; pgsql-general(at)postgresql(dot)org
> Subject: Re: [GENERAL] Rules, Triggers something more challenging
>
>
> Thank you for your suggestions Tamir.
>
> It is ok to make the business layer handle where the user can
> insert and
> what data. My problem is the security concern. The business layer
> (interface) is using ODBC (PostgreSQL) which is logging the login and
> password in a PLAIN TEXT file :(.

I wasn't envisioning the business layer being wrapped up with the user interface. If you wanted to, you could divide them into two distinct environments. A web front end that makes calls to a Python (my favorite) object which, in turn connects to PostgreSQL (not via odbc). In this scenario, you're business layer (the python code) could be used by the user layer to begin a transaction. The business layer object will get to PostgreSQL in a secure fashion, submit context information and retrieve context-specific data. It would then return it to the user layer with, possibly, some formatting to make it easy for the user layer to display it.

> Using this information
> anybody can access
> the database with the given login and password, and he would
> be able to
> access all the rown (insert into it) from the table the user
> is allowed to
> get access. That's the reason why I have to do on server side
> (data layer).
>
> I also tried to make a function and trigger but without luck.
> I don't know
> how to access trigger parameters from functions.
> create function verify_permission() returns integer as
> 'select user_id from permissions
> WHERE permissions.disco_id = NEW.disco_id
> AND permissions.username = CURRENT_USER' LANGUAGE SQL;
>
>
> CREATE TRIGGER verify_insert BEFORE INSERT ON visitors FOR EACH ROW
> EXECUTE PROCEDURE verify_permission('disco_id');

I wish I could help here with the syntax but all my db development experience is outside of PostgreSQL. I'm here to learn as well.

>
> Thank you for any help!
> -Peter
>
>
> ----- Original Message -----
> From: "Tamir Halperin" <tamir(at)brobus(dot)net>
> To: "Peter Csaba" <cpeter(at)webnova(dot)ro>; <pgsql-general(at)postgresql(dot)org>
> Sent: Thursday, April 03, 2003 8:52 PM
> Subject: RE: [GENERAL] Rules, Triggers something more challenging
>
>
> > I'd like to make a suggestion, Peter:
> >
> > You may very well find a way to contstrain inserts using
> pgsql according
> to your business rules, but I observe that you're beginning
> to develop a
> dependency on the data layer for your business logic.
> >
> > The reason you may not want to rely on db componentry
> (rules, triggers,
> etc...) to implement this type of business logic is because
> at some point in
> the future your business logic may change and then you're required to
> heavily modify your database when it may not be a problem
> with the data.
> >
> > Also, once you go down this road you begin to add more and
> more "data
> handling" code to your database and there are performance
> issues to consider
> there as well. Alternatively, having a business layer of
> software technology
> between your user interface and your database will probably
> have long term
> benefits in light of the problems I point out above.
> >
> > It appears to me that the user layer (interface) could ask
> for data that
> is within a context applicable to the user making the
> request. Then, only
> data that is within the user's context can be deleted or
> modified. This
> would be constrained by a combination of features in the user
> and business
> layers.
> >
> > Likewise, when the user is presented with an interface for inserting
> visitors, the business layer can take care of assigning
> context related
> information to the insert after the user is finished
> composing it in the
> user layer. The business layer can do this because it is
> managing the user
> layer's connection to the data layer and so it knows which user is
> attempting to insert data and, therefore, which context
> information should
> be included with the inserted data.
> >
> > How do these concerns and suggestions sound to you?
> >
> > Tamir
> >
> > > -----Original Message-----
> > > From: Peter Csaba [mailto:cpeter(at)webnova(dot)ro]
> > > Sent: Tuesday, April 01, 2003 10:54 AM
> > > To: pgsql-general(at)postgresql(dot)org
> > > Subject: [GENERAL] Rules, Triggers something more challenging
> > >
> > >
> > >
> > > 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.
>
>