Thanks for the explanation.
What do you mean with "inject" in 1/? ParameterizedSparqlString?
On Sun, Jul 5, 2020 at 8:53 PM Andy Seaborne <a...@apache.org> wrote:
>
> <_:label> is a syntax feature, not built into the storage or query
> execution.
>
> model.createResource("_:" + id));
>
> creates a resource with a strange URI (which is actually illegal by RFC
> 3986/7).
>
> There are various ways:
>
> 1/ The app can put the bnode into the QSM and injected at execution - it
> won't become a bnode-variable because that happens in parsing.
>
> 2/ To put a concrete node into a query:
>
> String bn = "<_:" + id+">";
>
> then put string into SPARQL syntax:
>
> QueryFactory.create("SELECT * { VALUES ?s {"+bn+"} ?s ?p ?o }");
> QueryFactory.create("SELECT * { "+bn+" ?p ?o }");
>
> 3/ rewrite the abstract syntax after parsing:
>
> Map<String, Resource> substitutions =
> Collections.singletonMap("s", bnode);
> query = QueryFactory.create("SELECT * { ?s ?p ?o }");
> query = QueryTransformOps.transformQuery(query, substitutions);
>
> Forms 2 and 3 have the advantage of not relying on how execution works -
> QSMs are ingested inthe start of execution and e.g. aren't visible in
> subqueries and also interact and bypass with query optimization.
>
> Andy
>
> On 05/07/2020 15:22, Martynas Jusevičius wrote:
> > Hi,
> >
> > I came across a situation where I want to carry over a blank node ID
> > in a QuerySolutionMap to QueryExecution, to match exact blank node
> > resources rather than have them as variables.
> >
> > I found an old thread by Holger on this topic:
> > https://mail-archives.apache.org/mod_mbox/jena-users/201308.mbox/browser
> >
> > The suggestion was to use <_:LABEL> URI scheme for blank nodes.
> > https://jena.apache.org/documentation/query/extension.html#blank-node-labels
> >
> > Based on that, I tried this logic:
> >
> > if (instance.isURIResource()) qsm.add(SPIN.THIS_VAR_NAME, instance);
> > if (instance.isAnon()) qsm.add(SPIN.THIS_VAR_NAME,
> > model.createResource("_:" + instance.getId()));
> >
> > However I'm not getting the results I expect. So I decided to make an
> > isolated test:
> >
> > @Test
> > public void bnodeQueryTest()
> > {
> > Model model = ModelFactory.createDefaultModel();
> > Resource bnode = model.createResource().addProperty(FOAF.name,
> > "whateverest");
> > AnonId id = bnode.getId();
> >
> > Query query = QueryFactory.create("SELECT * { ?s ?p ?o }");
> > QuerySolutionMap qsm = new QuerySolutionMap();
> > qsm.add("s", model.createResource("_:" + id));
> >
> > try (QueryExecution qex = QueryExecutionFactory.create(query,
> > model, qsm))
> > {
> > ResultSet resultSet = qex.execSelect();
> >
> > assertTrue(resultSet.hasNext());
> > assertEquals(id,
> > resultSet.next().get("s").asResource().getId());
> > }
> > }
> >
> > The test fails on assertTrue() because SELECT returns no results.
> >
> > Is the test flawed? Am I misunderstanding the use of this URI scheme?
> > If not, what's the purpose if it cannot match blank nodes in data?
> >
> > Martynas
> >
