Merge branch 'ad-freiburg:master' into add-prefilter-is-datatype

ad-freiburg · Feb 12, 2025 · edf4378 · edf4378
2 parents b58cc0b + 2fad765
commit edf4378
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Showing 2 changed files with 21 additions and 12 deletions.
diff --git a/src/engine/ExportQueryExecutionTrees.cpp b/src/engine/ExportQueryExecutionTrees.cpp
@@ -749,13 +749,10 @@ ad_utility::streams::stream_generator ExportQueryExecutionTrees::
   co_yield absl::StrCat(R"({"head":{"vars":)", jsonVars.dump(),
                         R"(},"results":{"bindings":[)");
 
+  // Get all columns with defined variables.
   QueryExecutionTree::ColumnIndicesAndTypes columns =
       qet.selectedVariablesToColumnIndices(selectClause, false);
   std::erase(columns, std::nullopt);
-  if (columns.empty()) {
-    co_yield "]}}";
-    co_return;
-  }
 
   auto getBinding = [&](const IdTable& idTable, const uint64_t& i,
                         const LocalVocab& localVocab) {
@@ -773,6 +770,8 @@ ad_utility::streams::stream_generator ExportQueryExecutionTrees::
     return binding.dump();
   };
 
+  // Iterate over the result and yield the bindings. Note that when `columns`
+  // is empty, we have to output an empty set of bindings per row.
   bool isFirstRow = true;
   uint64_t resultSize = 0;
   for (const auto& [pair, range] :
@@ -781,7 +780,11 @@ ad_utility::streams::stream_generator ExportQueryExecutionTrees::
       if (!isFirstRow) [[likely]] {
         co_yield ",";
       }
-      co_yield getBinding(pair.idTable_, i, pair.localVocab_);
+      if (columns.empty()) {
+        co_yield "{}";
+      } else {
+        co_yield getBinding(pair.idTable_, i, pair.localVocab_);
+      }
       cancellationHandle->throwIfCancelled();
       isFirstRow = false;
     }

diff --git a/test/ExportQueryExecutionTreesTest.cpp b/test/ExportQueryExecutionTreesTest.cpp
@@ -469,7 +469,14 @@ TEST(ExportQueryExecutionTrees, UnusedVariable) {
       "\n"
       "\n",
       makeExpectedQLeverJSON({std::nullopt, std::nullopt}),
-      makeExpectedSparqlJSON({}), expectedXml};
+      []() {
+        nlohmann::json j;
+        j["head"]["vars"].push_back("o");
+        j["results"]["bindings"].push_back({});
+        j["results"]["bindings"].push_back({});
+        return j;
+      }(),
+      expectedXml};
   runSelectQueryTestCase(testCase);
 
   // The `2` is the number of results including triples with UNDEF values. The
@@ -1061,8 +1068,7 @@ TEST(ExportQueryExecutionTrees, EmptyLines) {
                                []() {
                                  nlohmann::json j;
                                  j["head"]["vars"] = nlohmann::json::array();
-                                 j["results"]["bindings"] =
-                                     nlohmann::json::array();
+                                 j["results"]["bindings"].push_back({});
                                  return j;
                                }(),
                                expectedXml};
@@ -1257,13 +1263,13 @@ TEST(ExportQueryExecutionTrees, CornerCases) {
                                         ad_utility::MediaType::octetStream),
                ad_utility::Exception);
 
-  // A SparqlJSON query where none of the variables is even visible in the
-  // query body is not supported.
+  // If none of the selected variables is defined in the query body, we have an
+  // empty solution mapping per row, but there is no need to materialize any
+  // IRIs or literals.
   std::string queryNoVariablesVisible = "SELECT ?not ?known WHERE {<s> ?p ?o}";
   auto resultNoColumns = runJSONQuery(kg, queryNoVariablesVisible,
                                       ad_utility::MediaType::sparqlJson);
-  ASSERT_TRUE(resultNoColumns["results"]["bindings"].empty());
-
+  ASSERT_EQ(resultNoColumns["results"]["bindings"].size(), 1);
   auto qec = ad_utility::testing::getQec(kg);
   AD_EXPECT_THROW_WITH_MESSAGE(
       ExportQueryExecutionTrees::idToStringAndType(qec->getIndex(), Id::max(),