[Nepomuk] Result sorting with Nepomuk Querylib

[Sebastian Trüg]

On 09/18/2011 10:00 PM, Vishesh Handa wrote:
> 
> On Mon, Sep 19, 2011 at 12:52 AM, Sebastian Trüg <trueg at kde.org
> <mailto:trueg at kde.org>> wrote:
> 
>     On 09/18/2011 07:36 PM, Vishesh Handa wrote:
>     > Hey Sebastian
>     >
>     > I was working on my note taking application, and I want all the
>     > resources which are notes. So, I did this -
>     >
>     > Nepomuk::Query::ResourceTypeTerm typeTerm( Nepomuk::Types::Class(
>     > PIMO::Note() ) );
>     > Nepomuk::Query::Query query( typeTerm );
>     >
>     > which was fine. Then I realized that I wanted the notes to be sorted
>     > according to the last modification date.
>     >
>     > Currently, I'm doing this -
>     >
>     >     Nepomuk::Query::ResourceTypeTerm typeTerm( Nepomuk::Types::Class(
>     > PIMO::Note() ) );
>     >     Nepomuk::Query::Query query( typeTerm );
>     >
>     >     Nepomuk::Query::Query::RequestProperty rp(
>     NAO::lastModified(), false );
>     >     query.addRequestProperty( rp );
>     >
>     >     QString sparql = query.toSparqlQuery() + " order by
>     desc(?reqProp1)";
> 
>     Ahhhhhh, my eyes, I think I am blind!!!!!! :P
> 
> 
> :D
>  
> 
> 
>     This is what you do:
> 
>     ComparisonTerm term(NAO::lastModified(), Term());
>     term.setSortWeight(1, Qt::DescendingOrder);
>     Query query = ResourceTypeTerm(PIMO::Note()) && term;
> 
> 
> Now, why would anybody in their right mind think of using a
> ComparisonTerm, when one is not comparing anything?

Yeah, ComparisionTerm started out for plain comparision but turned out
into the general purpose term for anything that includes a property....
maybe a new name for 5.0?

> It would be so much easier to have something like -
> 
> Query q( term );
> q.addSortProperty( NAO::lastModified(), Qt::DescendingOrder ); // the
> weight is optional

You are right for this example. But think about sorting by some variable
somewhere down the graph. Artificial example:

ComparisionTerm t1(NAO::lastModified(), Term());
t1.setSortWeight(1);
ComparisionTerm t2(PIMO::isRelated(), t1);
Query q(t2);

How would you express that with your API? We could of course add a
shortcut/convenience method which internally creates a ComparisionTerm
(actually that is what requestproperties are now)...

Cheers,
Sebastian

>     and if you want the value of the date simply add:
>     term.setVariableName(QLatin1String("date"));
> 
>     and fetch it through Result::additionalBindings.
> 
>     Actually you can read it here:
>     http://api.kde.org/4.x-api/kdelibs-apidocs/nepomuk/html/classNepomuk_1_1Query_1_1ComparisonTerm.html#_details
> 
>     Cheers,
>     Sebastian
> 
>     >     client->sparqlQuery( sparql );
>     >
>     > Is it possible that you forgot to implement sorting in the query lib?
>     > Cause I can't seem to find how to do it.
>     >
>     > --
>     > Vishesh Handa
> 
> 
> 
> 
> -- 
> Vishesh Handa