Xapian discuss - Mar 2007 - Wildcard Query Help

Hi All

I've got a setting where I would like to do wildcard searches. I see  
that this can only be done with a Xapian::QueryParser and I am  
currently using Xapian::Query.

I tried to change my code over but when I change it to a  
Xapian::QueryParser it stops working. Now out of shear ignorance on  
my part, I've simply spaced my terms in a long string with spaces in  
between in the hopes that the QueryParser sorts them out. this might  
be my failure point. I have tried setting stemming to off etc.

	string matchField = "AUTHOR"; ( I have terms stored as  
"Xterm:AUTHOR:Terry Prachet"
	for (int j = 0; j != allMatchItems.size(); ++j) {
		fieldFilterMatchItems.push_back("Xterm:"+ matchField +":"
+
allMatchItems[j]);
		fieldFilterMatchItemsStr+= "Xterm:"+ matchField +":" +
allMatchItems
[j] + " ";
	}
			
	//THIS WORKS GREAT
	Xapian::Query fieldMatchFilter(Xapian::Query::OP_AND,  
fieldFilterMatchItems.begin(), fieldFilterMatchItems.end());
	if(query.empty()){query = fieldMatchFilter;}
	else{query = Xapian::Query(Xapian::Query::OP_AND, query,  
fieldMatchFilter);}

	//THIS FAILS TO GET ANY RESULTS
	QueryParser fieldTextQp;
	fieldTextQp.set_default_op(Xapian::Query::OP_AND);
	fieldTextQp.set_database(db);
	Xapian::Query fieldMatchFilter = fieldTextQp.parse_query 
(fieldFilterMatchItemsStr, Xapian::QueryParser::FLAG_WILDCARD);
	if(query.empty()){query = fieldMatchFilter;}
	else{query = Xapian::Query(Xapian::Query::OP_AND, query,  
fieldMatchFilter);}


I've also tried this which fails to to return any results

for (int j = 0; j != allMatchItems.size(); ++j) {
	QueryParser fieldTextQp;
	fieldTextQp.set_default_op(Xapian::Query::OP_AND);
	fieldTextQp.set_database(db);
	fieldTextQp.add_prefix(matchField, "Xterm:"+ matchField
+":");
	Xapian::Query fieldMatchFilter = fieldTextQp.parse_query 
(allMatchItems[j], Xapian::QueryParser::FLAG_WILDCARD);
	if(query.empty()){query = fieldMatchFilter;}
	else{query = Xapian::Query(Xapian::Query::OP_AND, query,  
fieldMatchFilter);}
}

Any pointers would be appreciated

Thanks

Colin

On Wed, Mar 14, 2007 at 03:39:10PM +0000, Colin Bell
wrote:
> I've got a setting where I would like to do wildcard searches. I see  
> that this can only be done with a Xapian::QueryParser and I am  
> currently using Xapian::Query.
> 
> I tried to change my code over but when I change it to a  
> Xapian::QueryParser it stops working. Now out of shear ignorance on  
> my part, I've simply spaced my terms in a long string with spaces in  
> between in the hopes that the QueryParser sorts them out. this might  
> be my failure point. I have tried setting stemming to off etc.
You need to tell the QueryParser what user-visible prefix to map to
the term prefix Xterm:AUTHOR: by using the add_boolean_prefix() or
add_prefix() method:

http://www.xapian.org/docs/apidoc/html/classXapian_1_1QueryParser.html#5afd438f9901fbd5005a92161c61d1c8

But I wouldn't recommend trying to programmatically build strings to pass to
the QueryParser - it's designed to parse human entered strings.

If you want to expand a wildcard in other circumstances, it's more robust
to just use Database::allterms_begin() like the QueryParser does internally:

http://article.gmane.org/gmane.comp.search.xapian.general/1724

Cheers,
    Olly