[Xapian-discuss] QueryParser (I think) question

[Olly Betts]

On Tue, May 22, 2007 at 04:08:54PM +0200, Andreas Marienborg wrote:
> On May 22, 2007, at 4:00 PM, James Aylett wrote:
> >On Tue, May 22, 2007 at 02:34:42PM +0200, Andreas Marienborg wrote:
> >
> >>so I tried the following: "source:1 OR source:2", but that results in
> >>the following query after
> >>parsing:
> >>
> >> Xapian::Query((or:(pos=1) FILTER (S1 AND S2)))
> >>
> >>is that expected? am I trying to do something that I cannot do? or am
> >>I just doing something wrong?
> >
> >It's not what I'd expect. The query parser came out of omega, whose
> >documentation states that boolean terms are combined by OR for similar
> >prefixes, then AND for the different prefixes to create the overall
> >FILTER clause. Looks like this documentation is no longer correct :-/

Actually, the "boolean terms" referred to there are ones specified as
"B" CGI parameters to Omega.  Boolean-prefixed terms in the QueryParser
post-date it being extracted from Omega by quite some time.

The QueryParser doesn't currently OR boolean-prefixed terms with the
same prefix, though there is a "FIXME" comment suggesting that it
probably should (in the absence of explicitly boolean operators that
is).

> But it is expected to ignore my OR and convert that to a "regular" term?
> 
> if I omit the OR it produces  Xapian::Query((S1 AND S2))
> 
> I have     $self->qp->set_default_op(OP_AND);
> 
> in my setup, but commenting it out does no difference.
> 
> 
> Is this a documentation problem, or a code-problem?

Both, I guess.  It's a known limitation of the current handling of
boolean prefixes in the QueryParser, which isn't mentioned in the
documentation.

Ironically, you can't currently use boolean prefixed terms in boolean
expressions.  Someone reported this to this list, I think late last
year but I can't find the mail currently.  Anyway, I couldn't see an
easy way to fix it at the time, but it's certainly something we should
fix, especially now 1.0.0 is out of the way.

Cheers,
    Olly