Fix simple literals returned as NULL using SERVICE (issue #1278)

[gitmpje]

Summary of changes

Fixes #1278 simple literals returned as NULL. The resolution uses same logic as here:

rdflib/rdflib/plugins/sparql/results/jsonresults.py

Lines 89 to 107 in 6f2c11c

	def parseJsonTerm(d):
	"""rdflib object (Literal, URIRef, BNode) for the given json-format dict.
	input is like:
	{ 'type': 'uri', 'value': 'http://famegame.com/2006/01/username' }
	{ 'type': 'literal', 'value': 'drewp' }
	"""
	t = d["type"]
	if t == "uri":
	return URIRef(d["value"])
	elif t == "literal":
	return Literal(d["value"], datatype=d.get("datatype"), lang=d.get("xml:lang"))
	elif t == "typed-literal":
	return Literal(d["value"], datatype=URIRef(d["datatype"]))
	elif t == "bnode":
	return BNode(d["value"])
	else:
	raise NotImplementedError("json term type %r" % t)

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Added tests for any changes that have a runtime impact.
• Checked that all tests and type checking passes.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[aucampia]

Thanks for the PR, a bit swamped fixing bugs and reviewing/fixing older PRs right now so I won't be able to take a detailed look until later, but it would be good to expand testing for SERVICE directive to ensure that each branch here is covered, which I'm not sure it will be, though I may be wrong.

[aucampia]

Also it seems your test is failing: https://github.com/RDFLib/rdflib/runs/6341689732?check_suite_focus=true#step:9:372

def test():
          """Test service returns simple literals not as NULL.
      
          Issue: https://github.com/RDFLib/rdflib/issues/1278
          """
      
          g = Graph()
          q = """SELECT ?s ?p ?o
      WHERE {
          SERVICE <https://dbpedia.org/sparql> {
              VALUES (?s ?p ?o) {(<http://example.org/a> <http://example.org/b> "c")}
          }
      }"""
  >       assert results.bindings[0].get(Variable("o")) == Literal("c")
  E       NameError: name 'results' is not defined

Accidentally clicked approve instead of comment.

[gitmpje]

Thanks for your support, the failing test should be fixed now. This test uses a similar approach as the existing SERVICE tests: https://github.com/RDFLib/rdflib/blob/eba13739e1d24b3e52697a1ec9545a361116951f/test/test_sparql/test_service.py. When I have time I will have a look at your suggestions for improving the test(s).

[coveralls]

Coverage increased (+0.02%) to 88.29% when pulling 6bd50f0 on gitmpje:issue1278_null_literals into 246c887 on RDFLib:master.

[aucampia]

Thanks for your support, the failing test should be fixed now. This test uses a similar approach as the existing SERVICE tests: https://github.com/RDFLib/rdflib/blob/eba13739e1d24b3e52697a1ec9545a361116951f/test/test_sparql/test_service.py. When I have time I will have a look at your suggestions for improving the test(s).

Okay in that case I think it is fine then, but maybe it would be good to add this test to test_service.py.

[gitmpje]

I added a more general test for different node types returned by a SERVICE clause to test_service.py.

[aucampia]

@gitmpje will review tonight, I don't think there are any issues with the code, but I may move tests around slightly, thank you for the PR.

[aucampia]

@gitmpje thanks for the PR. I added more tests to your branch and made some minor mostly cosmetic improvements, let me know if there are any concerns you have with the changes.

[gitmpje]

@gitmpje thanks for the PR. I added more tests to your branch and made some minor mostly cosmetic improvements, let me know if there are any concerns you have with the changes.

No concerns from my side, thank you for your comments and support!

[aucampia]

@RDFLib/core I will merge this by 2022-05-17 if there is no further feedback.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
2.8% Duplication