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

rdflib/plugins/sparql/evaluate.py

@@ -381,18 +381,22 @@ def _yieldBindingsFromServiceCallResult(ctx: QueryContext, r, variables):
     res_dict: Dict[Variable, Identifier] = {}
     for var in variables:
         if var in r and r[var]:
-            if r[var]["type"] == "uri":
-                res_dict[Variable(var)] = URIRef(r[var]["value"])
-            elif r[var]["type"] == "bnode":
-                res_dict[Variable(var)] = BNode(r[var]["value"])
-            elif r[var]["type"] == "literal" and "datatype" in r[var]:
+            d = r[var]
+            t = d["type"]
+            if t == "uri":
+                res_dict[Variable(var)] = URIRef(d["value"])
+            elif t == "literal":
                 res_dict[Variable(var)] = Literal(
-                    r[var]["value"], datatype=r[var]["datatype"]
+                    d["value"], datatype=d.get("datatype"), lang=d.get("xml:lang")
                 )
-            elif r[var]["type"] == "literal" and "xml:lang" in r[var]:
+            elif t == "typed-literal":
                 res_dict[Variable(var)] = Literal(
-                    r[var]["value"], lang=r[var]["xml:lang"]
+                    d["value"], datatype=URIRef(d["datatype"])
                 )
+            elif t == "bnode":
+                res_dict[Variable(var)] = BNode(d["value"])
+            else:
+                raise NotImplementedError("json term type %r" % t)
     yield FrozenBindings(ctx, res_dict)
 
 

test/test_issues/test_issue1278.py

@@ -0,0 +1,20 @@
+from test.utils import helper
+
+from rdflib import Graph, Literal, Variable
+
+
+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")}
+    }
+}"""
+    results = helper.query_with_retry(g, q)
+    assert results.bindings[0].get(Variable("o")) == Literal("c")

test/test_sparql/test_service.py

@@ -135,6 +135,32 @@ def test_service_with_implicit_select_and_allcaps():
     assert len(results) == 3
 
 
+def test_service_node_types():
+    """Test if SERVICE properly returns different types of nodes:
+    - URI;
+    - Simple Literal;
+    - Literal with datatype ;
+    - Literal with language tag .
+    """
+
+    g = Graph()
+    q = """
+SELECT ?o
+WHERE {
+    SERVICE <https://dbpedia.org/sparql> {
+        VALUES (?s ?p ?o) {
+            (<http://example.org/a> <http://example.org/uri> <http://example.org/URI>)
+            (<http://example.org/a> <http://example.org/simpleLiteral> "Simple Literal")
+            (<http://example.org/a> <http://example.org/dataType> "String Literal"^^xsd:string)
+            (<http://example.org/a> <http://example.org/language> "String Language"@en)
+        }
+    }
+    FILTER( ?o IN (<http://example.org/URI>, "Simple Literal", "String Literal"^^xsd:string, "String Language"@en) )
+}"""
+    results = helper.query_with_retry(g, q)
+    assert len(results) == 4
+
+
 # def test_with_fixture(httpserver):
 #    httpserver.expect_request("/sparql/?query=SELECT * WHERE ?s ?p ?o").respond_with_json({"vars": ["s","p","o"], "bindings":[]})
 #    test_server = httpserver.url_for('/sparql')
@@ -151,3 +177,4 @@ def test_service_with_implicit_select_and_allcaps():
     test_service_with_implicit_select()
     test_service_with_implicit_select_and_prefix()
     test_service_with_implicit_select_and_base()
+    test_service_node_types()