[Xapian-devel] Bug and patch for +terms with wildcards

[Olly Betts]

On Fri, Dec 08, 2006 at 06:44:56PM -0000, Richard Boulton wrote:
> > I think a better approach would be to allow Xapian::Query() to be
> > composed with other queries.  I know we used to allow this and it all
> > got out of hand, but that was because we tried to make it compose in
> > magic ways (e.g. Query() AND X would be X).  I'm just proposing that
> > this works in the obvious was for an empty query, and you've already
> > implemented this anyway!
> 
> I think the current behaviour of Xapian::Query() is good - it can't be
> composed, it returns an error if you try and use it, but it is useful as a
> placeholder when building up complex queries.  It's also not obvious to me
> whether Xapian::Query() should match all documents or no documents

It definitely matches no documents - try it!  If you call:

    enquire.set_query(Xapian::Query());
    Xapian::MSet mset = enquire.get_mset(0, 10);
    
Then mset.size() is 0.

> it depends whether you're thinking of searches as returning all documents
> which match a query, or thinking of a search as filtering the database to
> remove those documents which don't satisfy a query.

The former is how Xapian works so is the correct mental model to use.

Cheers,
    Olly