Xapian discuss - Nov 2008 - How to implement range searches?

Hi,

http://www.xapian.org/docs/queryparser.html states: "The QueryParser can 
be configured to support range-searching using document values."

How to do that using the Perl API?

I want to be able to search for "a:10..15 AND b:qaa..raa", that is
find
all documents where the value a is between 10 and 15 and b in the range 
qaa, qab, ..., qba, qbb, ..., qzz, raa.

Is that possible?

I think I have to store the values via $doc->add_value($valno, $value). 
But how do I tell the queryparser what value number to use for a given 
range? How do I tell it "a" is value number 3 and "b" is
number 5?

Do I understand it correctly that the range search is applied after the 
actual search? Does it mean the query above would lead to a complete 
scan over all documents since there is no search word in the query? Or 
is there an index also on the value fields of the documents?

Background: I want to store in the index 2 values. One is a string 
handle that says what process has brought the document into the index 
or updated it recently. The other is a UNIX timestamp.

Thanks,
Torsten

On Sun, Nov 16, 2008 at 01:26:12PM +0100, Torsten Foertsch
wrote:
> http://www.xapian.org/docs/queryparser.html states: "The QueryParser
can
> be configured to support range-searching using document values."
> 
> How to do that using the Perl API?
Much the same as in C++, except you can't currently create your own
subclasses in Perl - you are limited to the standard ones:

http://xapian.org/docs/valueranges.html
> I want to be able to search for "a:10..15 AND b:qaa..raa", that
is find
> all documents where the value a is between 10 and 15 and b in the range 
> qaa, qab, ..., qba, qbb, ..., qzz, raa.
> 
> Is that possible?
Yes (intermediate values such as qaabcde will also match the latter).
> Do I understand it correctly that the range search is applied after the 
> actual search?
Not really.  The matching all happens together, but the matcher is
fairly smart about what order to do things in within that.
> Does it mean the query above would lead to a complete 
> scan over all documents since there is no search word in the query?
Yes, and this can be a bit slow for such cases in 1.0.x.
> Or is there an index also on the value fields of the documents?
SVN trunk's chert backend stores values differently (much like how we
store term postings) and is much quicker.
> Background: I want to store in the index 2 values. One is a string 
> handle that says what process has brought the document into the index 
> or updated it recently. The other is a UNIX timestamp.
Does a range search really make sense on the first?  If not, then
indexing as a boolean term may be more sensible.  You can check for one
of several values still.

Cheers,
    Olly