fix: allow ordering by label in Gravsearch (DEV-2546) (#2798)

integration/src/test/scala/org/knora/webapi/responders/v2/SearchResponderV2Spec.scala

@@ -309,6 +309,33 @@ class SearchResponderV2Spec extends CoreSpec with ImplicitSender {
       }
     }
 
+    "perform an extended search ordered by label" in {
+
+      val queryAsc = searchResponderV2SpecFullData.constructQuerySortByLabel
+
+      appActor ! GravsearchRequestV2(
+        constructQuery = queryAsc,
+        targetSchema = ApiV2Complex,
+        schemaOptions = SchemaOptions.ForStandoffWithTextValues,
+        requestingUser = SharedTestDataADM.anonymousUser
+      )
+
+      val asc = expectMsgPF(timeout) { case response: ReadResourcesSequenceV2 => response }
+      assert(asc.resources.head.label == "A blue thing")
+
+      val queryDesc = searchResponderV2SpecFullData.constructQuerySortByLabelDesc
+
+      appActor ! GravsearchRequestV2(
+        constructQuery = queryDesc,
+        targetSchema = ApiV2Complex,
+        schemaOptions = SchemaOptions.ForStandoffWithTextValues,
+        requestingUser = SharedTestDataADM.anonymousUser
+      )
+
+      val desc = expectMsgPF(timeout) { case response: ReadResourcesSequenceV2 => response }
+      assert(desc.resources.head.label == "visible thing with hidden int values")
+    }
+
   }
 
 }

integration/src/test/scala/org/knora/webapi/responders/v2/SearchResponderV2SpecFullData.scala

@@ -417,4 +417,46 @@ class SearchResponderV2SpecFullData(implicit stringFormatter: StringFormatter) {
     querySchema = Some(ApiV2Simple)
   )
 
+  val constructQuerySortByLabel: ConstructQuery = ConstructQuery(
+    constructClause = ConstructClause(
+      Vector(
+        StatementPattern(
+          QueryVariable("r"),
+          IriRef("http://api.knora.org/ontology/knora-api/simple/v2#isMainResource".toSmartIri, None),
+          XsdLiteral("true", "http://www.w3.org/2001/XMLSchema#boolean".toSmartIri)
+        )
+      ),
+      querySchema = Some(ApiV2Simple)
+    ),
+    whereClause = WhereClause(
+      Vector(
+        StatementPattern(
+          QueryVariable("r"),
+          IriRef("http://www.w3.org/1999/02/22-rdf-syntax-ns#type".toSmartIri, None),
+          IriRef("http://0.0.0.0:3333/ontology/0001/anything/simple/v2#Thing".toSmartIri, None)
+        ),
+        StatementPattern(
+          QueryVariable("r"),
+          IriRef("http://www.w3.org/2000/01/rdf-schema#label".toSmartIri, None),
+          QueryVariable("l")
+        )
+      ),
+      Set(
+        QueryVariable("r"),
+        QueryVariable("l"),
+        IriRef("http://api.knora.org/ontology/knora-api/simple/v2#isMainResource".toSmartIri, None),
+        IriRef("http://www.w3.org/1999/02/22-rdf-syntax-ns#type".toSmartIri, None),
+        IriRef("http://0.0.0.0:3333/ontology/0001/anything/simple/v2#Thing".toSmartIri, None),
+        IriRef("http://www.w3.org/2000/01/rdf-schema#label".toSmartIri, None)
+      ),
+      querySchema = Some(ApiV2Simple)
+    ),
+    orderBy = Vector(OrderCriterion(QueryVariable("l"), true)),
+    querySchema = Some(ApiV2Simple)
+  )
+
+  val constructQuerySortByLabelDesc: ConstructQuery = constructQuerySortByLabel.copy(
+    orderBy = Vector(OrderCriterion(QueryVariable("l"), false))
+  )
+
 }

webapi/src/main/scala/org/knora/webapi/messages/util/search/gravsearch/prequery/AbstractPrequeryGenerator.scala

@@ -107,6 +107,9 @@ abstract class AbstractPrequeryGenerator(
   private var valueVariablesAutomaticallyGenerated: List[Map[QueryVariable, Set[GeneratedQueryVariable]]] =
     List(Map.empty[QueryVariable, Set[GeneratedQueryVariable]])
 
+  // Variables that point to actual literals; the only case currently would be rdfs:label
+  private var literalVariables: Set[QueryVariable] = Set.empty
+
   // Variables mentioned in the UNION block that is currently being processed, so we can ensure that a variable
   // is bound before it is used in a FILTER. This is a stack of sets, with one element per level of union blocks.
   private var variablesInUnionBlocks: List[Set[QueryVariable]] = List.empty
@@ -252,7 +255,7 @@ abstract class AbstractPrequeryGenerator(
 
         generatedVarsForOrderBy.headOption
 
-      case None => None
+      case None => if (literalVariables.contains(valueVar)) Some(valueVar) else None
     }
 
   // Generated statements for date literals, so we don't generate the same statements twice.
@@ -676,6 +679,13 @@ abstract class AbstractPrequeryGenerator(
     }
   }
 
+  private def recordLiteralVariables(statementPattern: StatementPattern): Unit =
+    statementPattern match {
+      case StatementPattern(_, IriRef(pred, None), obj: QueryVariable) if pred.toIri == OntologyConstants.Rdfs.Label =>
+        literalVariables += obj
+      case _ => ()
+    }
+
   protected def processStatementPatternFromWhereClause(
     statementPattern: StatementPattern,
     inputOrderBy: Seq[OrderCriterion],
@@ -719,6 +729,8 @@ abstract class AbstractPrequeryGenerator(
         // so we can make sure that they're defined before they're used in a FILTER pattern.
         recordVariablesInUnionBlock(statementPattern)
 
+        recordLiteralVariables(statementPattern)
+
         additionalStatementsForSubj ++ additionalStatementsForWholeStatement ++ additionalStatementsForObj
     }
   )

webapi/src/main/scala/org/knora/webapi/responders/v2/SearchResponderV2.scala

@@ -460,7 +460,7 @@ final case class SearchResponderV2Live(
 
       // Create a Select prequery
       querySchema <-
-        ZIO.fromOption(inputQuery.querySchema).orElseFail(AssertionException(s"WhereClause has no querySchema"))
+        ZIO.fromOption(inputQuery.querySchema).orElseFail(AssertionException(s"InputQuery has no querySchema"))
       gravsearchToPrequeryTransformer: GravsearchToPrequeryTransformer =
         new GravsearchToPrequeryTransformer(
           constructClause = inputQuery.constructClause,