Blank node URI scheme

[Martynas Jusevičius]

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