Xapian discuss - May 2007 - Returning special terms/postings

Hi,

  I was wondering if it is possible to return a particular indexed
term from a search result.  I have a special prefixed term index value
"XINDEX" which I store for each document I index (this differs from
the index value that xapian automatically adds at indexing time, and
is not necessarily unique).  I would like to return this index value,
instead of the actual document, as the result of a query.  The
prefixed term will not be included as a part of the query itself.  I
tried using termlist_begin() and get_termname() but I am either using
these wrongly or this does not work.  I want to return the term based
on its position in the termlist (i always index it at the first
position).

   Does this make sense?  Is this possible?

joe

On Mon, May 07, 2007 at 12:19:52PM +0900, Josef Novak
wrote:
> I was wondering if it is possible to return a particular indexed
> term from a search result.  I have a special prefixed term index value
> "XINDEX" which I store for each document I index (this differs
from
> the index value that xapian automatically adds at indexing time, and
> is not necessarily unique).  I would like to return this index value,
> instead of the actual document, as the result of a query.
Can you not just store it in the document data as well as adding it as a
term?  That's the simplest way and is likely to be most efficient.
> I tried using termlist_begin() and get_termname() but I am either
> using these wrongly or this does not work.
That should work.
> I want to return the term based
> on its position in the termlist (i always index it at the first
> position).
A TermIterator from termlist_begin() iterates over the terms in sorted
order.  The positions at which you added the terms (or indeed whether
they even have positional information) isn't relevant here.

So if you want to find a term with prefix "XINDEX", use (in C++):

    Xapian::TermIterator t = doc.termlist_begin();
    t.skip_to("XINDEX");
    if (t != doc.termlist_end()) {
	string term = *t;
	if (term.substr(0, 6) == "XINDEX") {
	    // term is the first XINDEX prefixed term
	}
    }

Cheers,
    Olly