Correct datatypes for string expressions

src/engine/ExportQueryExecutionTrees.cpp

@@ -14,6 +14,8 @@
 #include "util/ConstexprUtils.h"
 #include "util/http/MediaTypes.h"
 
+using LiteralOrIri = ad_utility::triple_component::LiteralOrIri;
+
 // Return true iff the `result` is nonempty.
 bool getResultForAsk(const std::shared_ptr<const Result>& result) {
   if (result->isFullyMaterialized()) {
@@ -347,11 +349,55 @@ ExportQueryExecutionTrees::idToStringAndTypeForEncodedValue(Id id) {
   }
 }
 
+// _____________________________________________________________________________
+std::optional<ad_utility::triple_component::Literal>
+ExportQueryExecutionTrees::idToLiteralForEncodedValue(
+    Id id, bool onlyReturnLiteralsWithXsdString) {
+  if (onlyReturnLiteralsWithXsdString) {
+    return std::nullopt;
+  }
+  auto optionalStringAndType = idToStringAndTypeForEncodedValue(id);
+  if (!optionalStringAndType) {
+    return std::nullopt;
+  }
+
+  return ad_utility::triple_component::Literal::literalWithoutQuotes(
+      optionalStringAndType->first);
+}
+
+// _____________________________________________________________________________
+bool ExportQueryExecutionTrees::isPlainLiteralOrLiteralWithXsdString(
+    const LiteralOrIri& word) {
+  return !word.hasDatatype() ||
+         asStringViewUnsafe(word.getDatatype()) == XSD_STRING;
+}
+
+// _____________________________________________________________________________
+std::optional<ad_utility::triple_component::Literal>
+ExportQueryExecutionTrees::handleIriOrLiteral(
+    LiteralOrIri word, bool onlyReturnLiteralsWithXsdString) {
+  if (!word.isLiteral()) {
+    AD_THROW("The input is an IRI, but only literals are allowed.");
+    return std::nullopt;
+  }
+
+  if (onlyReturnLiteralsWithXsdString) {
+    if (isPlainLiteralOrLiteralWithXsdString(word)) {
+      return word.getLiteral();
+    }
+    return std::nullopt;
+  }
+
+  if (word.hasDatatype() && !isPlainLiteralOrLiteralWithXsdString(word)) {
+    word.getLiteral().removeDatatype();
+  }
+  return word.getLiteral();
+}
+
 // _____________________________________________________________________________
 ad_utility::triple_component::LiteralOrIri
 ExportQueryExecutionTrees::getLiteralOrIriFromVocabIndex(
     const Index& index, Id id, const LocalVocab& localVocab) {
-  using LiteralOrIri = ad_utility::triple_component::LiteralOrIri;
   switch (id.getDatatype()) {
     case Datatype::LocalVocabIndex:
       return localVocab.getWord(id.getLocalVocabIndex()).asLiteralOrIri();
@@ -412,6 +458,39 @@ ExportQueryExecutionTrees::idToStringAndType(const Index& index, Id id,
       return idToStringAndTypeForEncodedValue(id);
   }
 }
+
+// _____________________________________________________________________________
+template <bool onlyReturnLiterals>
+std::optional<ad_utility::triple_component::Literal>
+ExportQueryExecutionTrees::idToLiteral(const Index& index, Id id,
+                                       const LocalVocab& localVocab,
+                                       bool onlyReturnLiteralsWithXsdString) {
+  using enum Datatype;
+  auto datatype = id.getDatatype();
+
+  if constexpr (onlyReturnLiterals) {
+    if (!(datatype == VocabIndex || datatype == LocalVocabIndex)) {
+      return std::nullopt;
+    }
+  }
+
+  switch (datatype) {
+    case WordVocabIndex:
+      return ad_utility::triple_component::Literal::literalWithoutQuotes(
+          index.indexToString(id.getWordVocabIndex()));
+    case VocabIndex:
+    case LocalVocabIndex:
+      return handleIriOrLiteral(
+          getLiteralOrIriFromVocabIndex(index, id, localVocab),
+          onlyReturnLiteralsWithXsdString);
+    case TextRecordIndex:
+      AD_THROW("TextRecordIndex case is not implemented.");
+      return std::nullopt;
+    default:
+      return idToLiteralForEncodedValue(id, onlyReturnLiteralsWithXsdString);
+  }
+}
+
 // ___________________________________________________________________________
 template std::optional<std::pair<std::string, const char*>>
 ExportQueryExecutionTrees::idToStringAndType<true, false, std::identity>(
@@ -433,6 +512,18 @@ ExportQueryExecutionTrees::idToStringAndType(const Index& index, Id id,
                                              const LocalVocab& localVocab,
                                              std::identity&& escapeFunction);
 
+// ___________________________________________________________________________
+template std::optional<ad_utility::triple_component::Literal>
+ExportQueryExecutionTrees::idToLiteral<false>(
+    const Index& index, Id id, const LocalVocab& localVocab,
+    bool onlyReturnLiteralsWithXsdString);
+
+// ___________________________________________________________________________
+template std::optional<ad_utility::triple_component::Literal>
+ExportQueryExecutionTrees::idToLiteral<true>(
+    const Index& index, Id id, const LocalVocab& localVocab,
+    bool onlyReturnLiteralsWithXsdString);
+
 // Convert a stringvalue and optional type to JSON binding.
 static nlohmann::json stringAndTypeToBinding(std::string_view entitystr,
                                              const char* xsdType) {

src/engine/ExportQueryExecutionTrees.h

@@ -21,6 +21,7 @@ class ExportQueryExecutionTrees {
  public:
   using MediaType = ad_utility::MediaType;
   using CancellationHandle = ad_utility::SharedCancellationHandle;
+  using LiteralOrIri = ad_utility::triple_component::LiteralOrIri;
 
   // Compute the result of the given `parsedQuery` (created by the
   // `SparqlParser`) for which the `QueryExecutionTree` has been previously
@@ -69,6 +70,37 @@ class ExportQueryExecutionTrees {
   static std::optional<std::pair<std::string, const char*>>
   idToStringAndTypeForEncodedValue(Id id);
 
+  // Convert the `id` to a 'LiteralOrIri. Datatypes are always stripped unless
+  // they are 'xsd:string', so for literals with non-'xsd:string' datatypes
+  // (this includes IDs that directly store their value, like Doubles) the
+  // datatype is always empty. If 'onlyReturnLiteralsWithXsdString' is true, all
+  // IRIs and literals with non'-xsd:string' datatypes (including encoded IDs)
+  // return 'std::nullopt'. These semantics are useful for the string
+  // expressions in StringExpressions.cpp.
+  template <bool returnOnlyLiterals = false>
+  static std::optional<ad_utility::triple_component::Literal> idToLiteral(
+      const Index& index, Id id, const LocalVocab& localVocab,
+      bool onlyReturnLiteralsWithXsdString = false);
+
+  // Same as the previous function, but only handles the datatypes for which the
+  // value is encoded directly in the ID. For other datatypes an exception is
+  // thrown.
+  // If `onlyReturnLiteralsWithXsdString` is `true`, returns `std::nullopt`.
+  // If `onlyReturnLiteralsWithXsdString` is `false`, removes datatypes from
+  // literals (e.g. the integer `42` is converted to the plain literal `"42"`).
+  static std::optional<ad_utility::triple_component::Literal>
+  idToLiteralForEncodedValue(Id id,
+                             bool onlyReturnLiteralsWithXsdString = false);
+
+  // A helper function for the `idToLiteralOrIri` function. Checks and processes
+  // a LiteralOrIri based on the given parameters.
+  static std::optional<ad_utility::triple_component::Literal>
+  handleIriOrLiteral(LiteralOrIri word, bool onlyReturnLiteralsWithXsdString);
+
+  // Checks if a LiteralOrIri is either a plain literal (without datatype)
+  // or a literal with the `xsd:string` datatype.
+  static bool isPlainLiteralOrLiteralWithXsdString(const LiteralOrIri& word);
+
   // Acts as a helper to retrieve an LiteralOrIri object
   // from an Id, where the Id is of type `VocabIndex` or `LocalVocabIndex`.
   // This function should only be called with suitable `Datatype` Id's,

src/engine/sparqlExpressions/SparqlExpressionValueGetters.cpp

@@ -90,6 +90,32 @@ std::optional<std::string> StringValueGetter::operator()(
   }
 }
 
+// ____________________________________________________________________________
+std::optional<ad_utility::triple_component::Literal>
+LiteralValueGetter::operator()(Id id, const EvaluationContext* context) const {
+  return ExportQueryExecutionTrees::idToLiteral(context->_qec.getIndex(), id,
+                                                context->_localVocab);
+}
+
+// ____________________________________________________________________________
+std::optional<ad_utility::triple_component::Literal>
+LiteralValueGetterWithXsdStringFilter::operator()(
+    Id id, const EvaluationContext* context) const {
+  return ExportQueryExecutionTrees::idToLiteral(context->_qec.getIndex(), id,
+                                                context->_localVocab, true);
+}
+
+// ____________________________________________________________________________
+std::optional<ad_utility::triple_component::Literal>
+LiteralValueGetterWithXsdStringFilter::operator()(
+    const LiteralOrIri& s, const EvaluationContext*) const {
+  if (ExportQueryExecutionTrees::isPlainLiteralOrLiteralWithXsdString(s)) {
+    return s.getLiteral();
+  }
+  AD_THROW("Input is not a plain string or xsd:string.");
+  return std::nullopt;
+}
+
 // ____________________________________________________________________________
 template <auto isSomethingFunction, auto prefix>
 Id IsSomethingValueGetter<isSomethingFunction, prefix>::operator()(

src/engine/sparqlExpressions/SparqlExpressionValueGetters.h

@@ -141,6 +141,45 @@ struct StringValueGetter : Mixin<StringValueGetter> {
   }
 };
 
+// This class can be used as the `ValueGetter` argument of Expression
+// templates. It produces a LiteralOrIri.
+struct LiteralValueGetter : Mixin<LiteralValueGetter> {
+  using Mixin<LiteralValueGetter>::operator();
+
+  std::optional<ad_utility::triple_component::Literal> operator()(
+      ValueId, const EvaluationContext*) const;
+
+  std::optional<ad_utility::triple_component::Literal> operator()(
+      const LiteralOrIri& s, const EvaluationContext*) const {
+    return s.getLiteral();
+  }
+};
+
+// Same as above but only literals with 'xsd:string' datatype or no datatype are
+// returned.
+struct LiteralValueGetterWithXsdStringFilter
+    : Mixin<LiteralValueGetterWithXsdStringFilter> {
+  using Mixin<LiteralValueGetterWithXsdStringFilter>::operator();
+
+  std::optional<ad_utility::triple_component::Literal> operator()(
+      ValueId, const EvaluationContext*) const;
+
+  std::optional<ad_utility::triple_component::Literal> operator()(
+      const LiteralOrIri& s, const EvaluationContext*) const;
+};
+
+// Value getter for `isBlank`.
+struct IsBlankNodeValueGetter : Mixin<IsBlankNodeValueGetter> {
+  using Mixin<IsBlankNodeValueGetter>::operator();
+  Id operator()(ValueId id, const EvaluationContext*) const {
+    return Id::makeFromBool(id.getDatatype() == Datatype::BlankNodeIndex);
+  }
+
+  Id operator()(const LiteralOrIri&, const EvaluationContext*) const {
+    return Id::makeFromBool(false);
+  }
+};
+
 // Boolean value getter that checks whether the given `Id` is a `ValueId` of the
 // given `datatype`.
 template <Datatype datatype>