Re: [HACKERS] ALTER TABLE ( smallinto -> boolean ) ...

Marc G. Fournier wrote:

> Moved off of -hackers, since its long gotten out of that realm :)
>
> On Thu, 1 Sep 2005, Tom Lane wrote:
>
> > "Marc G. Fournier" <scrappy@postgresql.org> writes:
> >> On Mon, 29 Aug 2005, Tom Lane wrote:
> >>> No, because there's no built-in cast from smallint to bool.
> >
> >> 'k, I just took a read through the "CREATE CAST" man page,
> and don't think
> >> I can use that for this,
> >
> > Sure you can.  Make a SQL or PLPGSQL function that does the
> conversion
> > you want and then create a cast using it.
>
> Ah, okay, I just re-read the man page and think I stumbled
> upon what I
> overlooked the first time ...
>
> all I want to do is:
>
> CREATE CAST ( 0 AS boolean )
>         WITH FUNCTION <I have to create this>
>           AS ASSIGNMENT;
>
> And then each time I try to insert a '0' into a BOOLEAN
> field, it will
> auto convert that (based on my function) to 'f' ...
>
> And I'd need to do a second one for 1 -> 't' ...
>
> Am I reading it right this time ... ?

Here's what I'm using:

CREATE OR REPLACE FUNCTION int2bool (INTEGER) RETURNS BOOLEAN AS $$ SELECT ($1 != 0);
$$ LANGUAGE 'SQL' IMMUTABLE STRICT;

CREATE OR REPLACE FUNCTION bool2int (BOOLEAN) RETURNS INTEGER AS $$ SELECT CASE WHEN $1 THEN 1             WHEN NOT $1
THEN0             ELSE NULL END; 
$$ LANGUAGE 'SQL' IMMUTABLE STRICT;

CREATE CAST (INTEGER AS BOOLEAN) WITH FUNCTION int2bool (INTEGER) AS ASSIGNMENT;

CREATE CAST (BOOLEAN AS INTEGER) WITH FUNCTION bool2int (BOOLEAN) AS ASSIGNMENT;

done.

Owen