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Posted to users@jena.apache.org by Laurent Pellegrino <la...@gmail.com> on 2011/05/23 15:38:45 UTC

Union of two ResultSet

Hi all,

Does Jena provide a means to create a new ResultSet which is the union
of two ResultSets? Especially in the case where the two result sets
have the same variables. Or is there a means to create a ResultSet by
using a list of variables and a QuerySolution/Binding?

I have take a look at ResultSetUtils and ResultSetMem but it seems
there is nothing to do it :S

Kind Regards,

Laurent

Re: Union of two ResultSet

Posted by Laurent Pellegrino <la...@gmail.com>.

Thanks for your help. It seems the first solution is the simplest.
However, I do not get a ResultSet object as result.

Regarding the second solution, I have taken a look at the
ResultSetStream constructor and it seems we need 3 parameters:

* the first one is a lists of variable: we just have to append the
variables from the two result sets
* the second is a Model: it seems we can create a new model that is
the concatenation of the two models
ModelFactory.createDefaultModel().add(...)
* the third is a QueryIterator: I can create a QueryIterConcat but we
need to specify a parameter which is an ExecutionContext, what is the
value to use for it?

It seems it is not really easy and efficient (due to the concatenation
of models). Moreover, It would be nice if the solution works for any
kind of ResultSet.

I have proposed a small patch for it. See
https://issues.apache.org/jira/browse/JENA-66.

Laurent

>> Does Jena provide a means to create a new ResultSet which is the union
>> of two ResultSets? Especially in the case where the two result sets
>> have the same variables.
>
> No - there isn't specifically.
>
> UNION is concatenation and results are Iterator<QuerySolution>.  You could
> use Iter.concat or your favourite way to concatenate iterators.
>
>> Or is there a means to create a ResultSet by
>> using a list of variables and a QuerySolution/Binding?
>
> You could create a QueryIterator and use ResultSetStream
>
> There are lots QueryIterator including QueryIterConcat
>
> Internally, everything is done in QueryIterator - ResultSets are the final
> step of presentation.
>
>> I have take a look at ResultSetUtils and ResultSetMem but it seems
>> there is nothing to do it :S
>>
>> Kind Regards,
>>
>> Laurent
>
>        Andy
>

Re: Union of two ResultSet

Posted by Andy Seaborne <an...@epimorphics.com>.

On 23/05/11 14:38, Laurent Pellegrino wrote:
> Hi all,
>
> Does Jena provide a means to create a new ResultSet which is the union
> of two ResultSets? Especially in the case where the two result sets
> have the same variables.

No - there isn't specifically.

UNION is concatenation and results are Iterator<QuerySolution>.  You 
could use Iter.concat or your favourite way to concatenate iterators.

> Or is there a means to create a ResultSet by
> using a list of variables and a QuerySolution/Binding?

You could create a QueryIterator and use ResultSetStream

There are lots QueryIterator including QueryIterConcat

Internally, everything is done in QueryIterator - ResultSets are the 
final step of presentation.

> I have take a look at ResultSetUtils and ResultSetMem but it seems
> there is nothing to do it :S
>
> Kind Regards,
>
> Laurent

	Andy