Re: Savepoints in PL/pgSQL

On Dec 19, 4:16 pm, maili...@oopsware.de (Bernd Helmle) wrote:
> On 19 Dec 2006 07:05:10 -0800, "BigSmoke" <bigsm...@gmail.com> wrote:
>
> > I understand that due to a lack of nested transaction support, it is
> > not possible to use START TRANSACTION within a PL/PgSQL function. What
> > I, however, do not understand is why I can't use SAVEPOINT either. I'm
> > writing long test functions wherein, at the start of the function, I'd
> > like to define all test data followed by a "SAVEPOINT
> > fresh_test_data;". Will this become possible in the (near) future? I
> > mean, savepoints are of limited use to me if they imply that I can't
> > stick my tests in stored procedures.Use
>
> BEGIN
>
>   ...
>
> EXCEPTION
>
>   ...
>
> END;
>
> Blocks instead. The pl/pgsql exception handling is implemented on top
> of PostgreSQL's SAVEPOINT infrastructure. We are lacking user defined
> exception support, but you can raise generic errors with RAISE EXCEPTION.

I can't solve my problem with a BEGIN EXCEPTION END block because of
what I do in these functions. Here's an example function.

CREATE OR REPLACE FUNCTION test_something() RETURNS VOID AS $$
BEGIN
  -- Define some test data

  -- SAVEPOINT fresh_test_data; -- If only I could ...

  IF some_test_assertion_fails THEN
    RAISE EXCEPTION 'Some informative message';
  END IF;

  -- ROLLBACK TO SAVEPOINT fresh_test_data;
END;
$$ LANGUAGE plpgsql;

In these functions, I raise an exception whenever a test fails. Now, If
I want to create an implicit savepoint using BEGIN/END blocks around
individual tests, I don't see how I can still sanely preserve this
behavior without the most horrid of hacks. The following code is what I
think I would need to do to emulate savepoints without direct access to
them. :-(  (I hope that I'm missing something.)

CREATE OR REPLACE FUNCTION test_something() RETURNS VOID AS $$
BEGIN
  -- Define some test data

  BEGIN
    -- This is a useful test ;-)
    IF TRUE THEN
      RAISE EXCEPTION 'Aaargh! The test failed!';
    END IF;

    RAISE EXCEPTION '__dummy_restore_state__';

  EXCEPTION WHEN raise_exception THEN
    IF SQLERRM != '__dummy_restore_state__' THEN
      RAISE EXCEPTION '%', SQLERRM;
    END IF;
  END;
END;
$$ LANGUAGE plpgsql;