Re: [HACKERS] dumping rules

Jan,

I'm absolutely amazed by this piece of magic.

I updated postrgreSQL from CVS, built postgres and the get_ruledef()
function and gave it a try.

A simple VIEW I have goes in as:-

SELECT t.artist, t.song, t.trackno, d.cdname
FROM disks d, tracks t
WHERE d.diskid = t.diskid

And comes out as :-

disks=> select get_ruledef('_RETsongs');
get_ruledef
--------------------------------------------------------------------------------
---------------------------------------------------------------------
CREATE RULE _RETsongs AS ON SELECT TO songs DO INSTEAD SELECT t.artist, t.song,
t.trackno, d.cdname FROM disks d, tracks t WHERE d.diskid = t.diskid;
(1 row)

disks=>

Absolutely perfect rule definition for the VIEW.

One slight bug I found was that ANDs come out as ORs but that's
easily fixed with the following patch.

What can I say.....
Thanks,
Keith.

*** get_ruledef/get_ruledef.c.orig Tue Aug 18 19:34:34 1998
--- get_ruledef/get_ruledef.c Tue Aug 18 19:34:53 1998
***************
*** 738,744 ****
strcat(buf, get_rule_expr(rtable, rt_index,
(Node *)get_leftop(expr),
varprefix));
! strcat(buf, ") OR (");
strcat(buf, get_rule_expr(rtable, rt_index,
(Node *)get_rightop(expr),
varprefix));
--- 738,744 ----
strcat(buf, get_rule_expr(rtable, rt_index,
(Node *)get_leftop(expr),
varprefix));
! strcat(buf, ") AND (");
strcat(buf, get_rule_expr(rtable, rt_index,
(Node *)get_rightop(expr),
varprefix));

jwieck(at)debis(dot)com (Jan Wieck)
> >
> > > emkxp01(at)mtcc(dot)demon(dot)co(dot)uk
> > > Jan,
> > >
> > > Whilst you are working on the rules system it would be nice if
> > > you could look for an oportunity to store the plain text rule
> > > definition at creation time.
> > >
> > > If the definition were stored in a table column it would allow us
> > > to dump and restore databases in a more complete way.
> > >
> > > I looked at this some while ago myself but never got close to
> > > making it work.
> > >
> > > Keith.
> > >
> >
> > Yes, that would really be nice and I had something the like
> > already in mind.
> >
> > [...]
> > On the other hand wouldn't it be too complicated to
> > reconstruct a command from the parsetree, that exactly
> > creates the rule. Reading a parsetree isn't fun, but after
> > all I did on the rewrite system I'm somewhat familiar with it
> > now (sometimes I see the cup in a targetlist, the coffee
> > machine in the rangetable and all the buttons in the
> > qualification when pulling a coffee out of it - think I
> > should I consult a psychist when the rule system is fixed
> > :-).
> >
> >
> > Jan
>
> To demonstrate that it really isn't that complicated as it
> looks, here is a C function that if defined in the backend as
>
> CREATE FUNCTION get_ruledef(name)
> RETURNS text AS '.../get_ruledef.so'
> LANGUAGE 'C';
>
> can be used to see a textual representation of the rule given
> as argument.