Thread: information_schema for all users

I wold like to make a plpgsql function that return column names and
their data types of a specific table.
I have done this using:

CREATE OR REPLACE FUNCTION _get_table_definition(refcursor) RETURNS
refcursor SECURITY DEFINER AS
$$
DECLARE
BEGIN   OPEN $1 FOR SELECT column_name as field_name, data_type as
field_type FROM information_schema.columns WHERE
table_name='_table_name';   RETURN $1;
END;
$$ LANGUAGE plpgsql;

but it works only with the database owner although i have used
"SECURITY DEFINER".
How can I make it works for everyone that calls the function?

I use PostgreSQL 8.1.4

On Sun, Jul 09, 2006 at 09:52:35AM +0200, Luca Giandoso wrote:
> I wold like to make a plpgsql function that return column names and
> their data types of a specific table.

Do you have a reason for returning a cursor instead of SETOF some
type?  In versions prior to 8.1 you could create a custom type for
the return columns; in 8.1 you could use OUT parameters and return
SETOF record.

[snip function that returns a cursor over information_schema.columns]

> but it works only with the database owner although i have used
> "SECURITY DEFINER".

The information_schema privilege checks are based on current_user,
which is apparently evaluated when you fetch rows from the cursor,
not when you open the cursor.  Here's a simple example; we'll create
the following function as user alice:
 CREATE FUNCTION testfunc(refcursor) RETURNS refcursor AS $$ BEGIN     RAISE INFO 'current_user = %', current_user;
OPEN$1 FOR SELECT current_user;     RETURN $1; END; $$ LANGUAGE plpgsql SECURITY DEFINER;
 

First we'll call the function as alice; notice that the current_user
displayed by the RAISE statement is the same as the current_user
fetched by the cursor:
 test=> BEGIN; SELECT testfunc('curs'); FETCH curs; COMMIT; BEGIN INFO:  current_user = alice  testfunc  ----------
curs(1 row)   current_user  --------------  alice (1 row)  COMMIT
 

Now we'll call the same function as user bob; notice that the
current_user displayed by the RAISE statement is "alice" because
of SECURITY DEFINER but that the current_user displayed when fetching
from the cursor is "bob":
 test=> \c - bob Password for user bob:  You are now connected as new user "bob". test=> BEGIN; SELECT
testfunc('curs');FETCH curs; COMMIT; BEGIN INFO:  current_user = alice  testfunc  ----------  curs (1 row)
current_user --------------  bob (1 row)  COMMIT
 

I don't know if this behavior is intentional but that's how it
currently works.  You could avoid it by returning SETOF some type
rather than a cursor, or you could query the PostgreSQL system
catalogs directly instead of using information_schema.  If you're
returning the results of a simple query, and if you can make that
query work without SECURITY DEFINER, then you could use a view
instead of a function.

-- 
Michael Fuhr