Thanks Holger. I ended up using SPINFactory.isVariable() and
SPINFactory.asVariable().
I also realized afterwards that I need a recursive check, so the final
version of my method was this:
protected boolean isWhereVariable(Variable var)
{
return ResourceUtils.reachableClosure(getWhere()).
listSubjectsWithProperty(SP.varName, var.getName()).
hasNext();
}
Will check SPINUtil.
Martynas
graphity.org
2013 m. gegužė 23 d., ketvirtadienis 02:21:28 UTC+3, Holger Knublauch rašė:
>
> On 5/23/2013 0:53, [email protected] <javascript:> wrote:
> > Hey,
> >
> > I'm working on a SPIN-based query builder. One of the last things I
> > added is a possibility to specify a Variable or expression to be used
> > in ORDER BY.
> > This is working fine, except that the supplied Variable might not be
> > used in the WHERE pattern, which produces an invalid SPARQL query.
> >
> > I want to fix this by checking if the supplied Variable is present in
> > the WHERE pattern, and throw an exception if it's not. The method I'm
> > using:
> >
> > protected boolean isWhereVariable(Variable var)
> > {
> > Iterator<Element> it = getWhere().getElements().iterator();
> >
> > while (it.hasNext())
> > {
> > Element element = it.next();
> >
> > RDFNode subject =
> > element.getRequiredProperty(SP.subject).getObject();
> > if (subject.canAs(Variable.class) &&
> > subject.as(Variable.class).getName().equals(var.getName()))
> > return true;
> >
> > RDFNode predicate =
> > element.getRequiredProperty(SP.predicate).getObject();
> > if (predicate.canAs(Variable.class) &&
> > predicate.as(Variable.class).getName().equals(var.getName()))
> > return true;
> >
> > RDFNode object =
> > element.getRequiredProperty(SP.object).getObject();
> > if (object.canAs(Variable.class) &&
> > object.as(Variable.class).getName().equals(var.getName()))
> > return true;
> > }
> >
> > return false;
> > }
> >
> > The problem is that subject.canAs(Variable.class) returns false, even
> > if stepping through the code I can see, that
> > subject.as(Variable.class) is "?instance" for example (the variable
> > I'm expecting).
> > Any ideas on why the canAs() check doesn't work, or how this could be
> > implemented in a better way?
>
> canAs() probably relies on an rdf:type triple, but Variables usually
> don't have those. Instead use SPINFactory.isVariable(node).
>
> The loop above looks rather fragile though because it only handles BGPs,
> i.e. nested blocks would be ignored. This may work in your specific
> case, but instead you may want to do a recursive traversal. I believe
> the following does something close to what you need (from SPINUtil):
>
> public static Integer containsThis(CommandWithWhere command) {
> return new ContainsVarChecker(SPIN._this).checkDepth(command);
> }
>
> HTH
> Holger
>
>
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