implement SPARQL Ask

sparql/src/exec.rs

@@ -135,6 +135,16 @@ impl<'a, D: Dataset> ExecState<'a, D> {
         }
     }
 
+    pub fn ask(
+        &mut self,
+        pattern: &GraphPattern,
+        graph_matcher: &[Option<ArcTerm>],
+        binding: Option<&Binding>,
+    ) -> Result<bool, SparqlWrapperError<D::Error>> {
+        self.select(pattern, graph_matcher, binding)
+            .map(|binding| binding.into_iter().next().is_some())
+    }
+
     fn bgp(
         &mut self,
         patterns: &[TriplePattern],

sparql/src/test.rs

@@ -14,15 +14,24 @@ use test_case::test_case;
     vec!["<http://schema.org/name>", "<http://schema.org/name>", "<http://schema.org/performerIn>", "<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>", "<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>", ];
     "predicates"
 )]
-fn test_select_1(query: &str, exp: Vec<&str>) -> TestResult {
+#[test_case(
+    "SELECT ?x { ?x ?y \"not in the repo\" }",
+    vec![];
+    "no result"
+)]
+fn test_select_1_and_ask(query: &str, exp: Vec<&str>) -> TestResult {
     let dataset = dataset_101()?;
     let dataset = SparqlWrapper(&dataset);
-    let query = SparqlQuery::parse(query)?;
-    let bindings = dataset.query(&query)?.into_bindings();
+    let parsed_query = SparqlQuery::parse(query)?;
+    let bindings = dataset.query(&parsed_query)?.into_bindings();
     assert_eq!(bindings.variables(), &["x"]);
     let mut got = bindings_to_vec(bindings);
     got.sort();
     assert_eq!(exp, got);
+
+    let parsed_query = SparqlQuery::parse(&query.replace("SELECT ?x", "ASK"))?;
+    let response = dataset.query(&parsed_query)?.into_boolean();
+    assert_eq!(response, !exp.is_empty());
     Ok(())
 }
 

sparql/src/wrapper.rs

@@ -58,7 +58,12 @@ impl<'a, D: Dataset> SparqlDataset for SparqlWrapper<'a, D> {
                 dataset,
                 pattern,
                 base_iri,
-            } => Err(SparqlWrapperError::NotImplemented("ASK query")),
+            } => {
+                let mut exec = ExecState::new(self.0, dataset)?;
+                let cfg = exec.config_cloned();
+                exec.ask(pattern, &cfg.default_matcher, None)
+                    .map(SparqlResult::Boolean)
+            }
         }
     }
 }