Xapian discuss - Sep 2006 - QueryParser, mapping a single prefix to multiple fields ?

Hello,

The doc for QueryParser::add_prefix and QueryParser::add_boolean_prefix 
says that "multiple fields can be mapped to the same prefix", which is
very convenient to handle aliases.

But I am in the opposite situation where I would like to map a same 
prefix to multiple fields: for example, a search for 'title:xapian' 
would look for 'XTITLEFRExapian' or 'XTITLEENGxapian'.

What would be the best way to achieve this? (I'm using the PHP bindings)

 From what I see, this is not something which is currently supported. If 
I call multiple times add_boolean_prefix with the same 'field', only the
first prefix is taken into account.

A solution would be to 'duplicate' search terms, adding a prefix like 
'XTITLE ENG AND FRE', but this is obviously a waste of resources.

For now, the only solution I see is to pre-process the user request 
before giving it to the query parser (replace "title:something" with 
"titleeng:something OR titlefre:something" for each field I want to 
handle like this)... which is not very elegant.

Perhaps it would be a useful feature to add to the query parser? It 
would not break the API (just call add_prefix / add_boolean_prefix 
several times with the same field and different prefixes) and I don't 
think it would break any existing code.

Of course ;-) , I'm not fluent enough in C++ to code that myself, and I 
don't even know if I ask for a simple change or a big one!

Please let me know...

Best regards,

Daniel

On Wed, Sep 13, 2006 at 12:34:51PM +0200, Daniel M?nard
wrote:
> From what I see, this is not something which is currently supported. If 
> I call multiple times add_boolean_prefix with the same 'field',
only the
> first prefix is taken into account.
That's a bug - calling add_boolean_prefix() a second time should change
the prefix.  But I failed to remember how std::map::insert() works in this
case (we've had a previous bug because of this too sadly - I think I
need to go and audit all calls to std::map::insert()).
> Perhaps it would be a useful feature to add to the query parser? It 
> would not break the API (just call add_prefix / add_boolean_prefix 
> several times with the same field and different prefixes) and I don't 
> think it would break any existing code.
It shouldn't break existing code (since add_prefix and add_boolean_prefix
currently don't work as intended when called a second time) but it would
make it impossible to change the registered prefixes, and having to
start from a fresh QueryParser is a pain if you just want to change one
setting.

But it's not an unreasonable thing to want to do, and I think it should
be possible to allow it.  I'm in the middle of trying to sort out UTF-8 
right now - can you file a wishlist bug so this doesn't get forgotten?

Cheers,
    Olly