Allow selecting all variables as payload in spatial search SERVICE (a…

…d-freiburg#1656)

In the spatial search service (triggered via `SERVICE spatialSearch:`) all variables from the right hand side of the join (except for the join column) that shall be part of the result have to be explicitly selected via the `<payload>` parameter. This PR adds a special value `<all>` for this parameter, which automatically selects all the variables from the right side as payload.

src/engine/SpatialJoin.cpp

@@ -175,30 +175,24 @@ string SpatialJoin::getDescriptor() const {
 // ____________________________________________________________________________
 size_t SpatialJoin::getResultWidth() const {
   if (childLeft_ && childRight_) {
-    // Helper visitor lambda to determine the size of the right child after
-    // selecting only the join column and explicitly requested payload columns
-    auto sizeRight = [this]<typename T>(const T& value) {
-      if constexpr (std::is_same_v<T, PayloadAllVariables>) {
-        return childRight_->getResultWidth();
-      } else {
-        static_assert(std::is_same_v<T, std::vector<Variable>>);
-
-        // We convert to a set here, because we allow multiple occurrences of
-        // variables in payloadVariables_
-        absl::flat_hash_set<Variable> pvSet{value.begin(), value.end()};
-
-        // The payloadVariables_ may contain the right join variable
-        return pvSet.size() + (pvSet.contains(config_.right_) ? 0 : 1);
-      }
-    };
-
     // don't subtract anything because of a common join column. In the case
     // of the spatial join, the join column is different for both sides (e.g.
     // objects with a distance of at most 500m to each other, then each object
     // might contain different positions, which should be kept).
     // For the right join table we only use the selected columns.
-    auto widthChildren = childLeft_->getResultWidth() +
-                         std::visit(sizeRight, config_.payloadVariables_);
+    size_t sizeRight;
+    if (config_.payloadVariables_.isAll()) {
+      sizeRight = childRight_->getResultWidth();
+    } else {
+      // We convert to a set here, because we allow multiple occurrences of
+      // variables in payloadVariables_
+      std::vector<Variable> pv = config_.payloadVariables_.getVariables();
+      absl::flat_hash_set<Variable> pvSet{pv.begin(), pv.end()};
+
+      // The payloadVariables_ may contain the right join variable
+      return pvSet.size() + (pvSet.contains(config_.right_) ? 0 : 1);
+    }
+    auto widthChildren = childLeft_->getResultWidth() + sizeRight;
 
     if (config_.distanceVariable_.has_value()) {
       return widthChildren + 1;
@@ -324,34 +318,29 @@ VariableToColumnMap SpatialJoin::getVarColMapPayloadVars() const {
                     "Child right must be added before payload variable to "
                     "column map can be computed.");
 
-  auto payloadVariablesVisitor = [this]<typename T>(const T& value) {
-    const auto& varColMap = childRight_->getVariableColumns();
-    VariableToColumnMap newVarColMap;
+  const auto& varColMap = childRight_->getVariableColumns();
+  VariableToColumnMap newVarColMap;
 
-    if constexpr (std::is_same_v<T, PayloadAllVariables>) {
-      newVarColMap = VariableToColumnMap{varColMap};
-    } else {
-      static_assert(std::is_same_v<T, std::vector<Variable>>);
-      for (const auto& var : value) {
-        if (varColMap.contains(var)) {
-          newVarColMap.insert_or_assign(var, varColMap.at(var));
-        } else {
-          addWarningOrThrow(
-              absl::StrCat("Variable '", var.name(),
-                           "' selected as payload to spatial join but not "
-                           "present in right child."));
-        }
+  if (config_.payloadVariables_.isAll()) {
+    newVarColMap = VariableToColumnMap{varColMap};
+  } else {
+    for (const auto& var : config_.payloadVariables_.getVariables()) {
+      if (varColMap.contains(var)) {
+        newVarColMap.insert_or_assign(var, varColMap.at(var));
+      } else {
+        addWarningOrThrow(
+            absl::StrCat("Variable '", var.name(),
+                         "' selected as payload to spatial join but not "
+                         "present in right child."));
       }
-      AD_CONTRACT_CHECK(
-          varColMap.contains(config_.right_),
-          "Right variable is not defined in right child of spatial join.");
-      newVarColMap.insert_or_assign(config_.right_,
-                                    varColMap.at(config_.right_));
     }
-    return newVarColMap;
-  };
+    AD_CONTRACT_CHECK(
+        varColMap.contains(config_.right_),
+        "Right variable is not defined in right child of spatial join.");
+    newVarColMap.insert_or_assign(config_.right_, varColMap.at(config_.right_));
+  }
 
-  return std::visit(payloadVariablesVisitor, config_.payloadVariables_);
+  return newVarColMap;
 }
 
 // ____________________________________________________________________________

src/engine/SpatialJoin.h

@@ -11,6 +11,7 @@
 
 #include "engine/Operation.h"
 #include "global/Id.h"
+#include "parser/PayloadVariables.h"
 #include "parser/data/Variable.h"
 
 // A nearest neighbor search with optionally a maximum distance.
@@ -27,18 +28,6 @@ struct MaxDistanceConfig {
 // Configuration to restrict the results provided by the SpatialJoin
 using SpatialJoinTask = std::variant<NearestNeighborsConfig, MaxDistanceConfig>;
 
-// Represents the selection of all variables of the right join table as payload
-struct PayloadAllVariables : std::monostate {
-  bool operator==([[maybe_unused]] const std::vector<Variable>& other) const {
-    return false;
-  };
-};
-
-// Configuration to select which columns of the right join table should be
-// part of the result.
-using PayloadVariables =
-    std::variant<PayloadAllVariables, std::vector<Variable>>;
-
 // Selection of a SpatialJoin algorithm
 enum class SpatialJoinAlgorithm { BASELINE, S2_GEOMETRY, BOUNDING_BOX };
 const SpatialJoinAlgorithm SPATIAL_JOIN_DEFAULT_ALGORITHM =
@@ -60,7 +49,7 @@ struct SpatialJoinConfiguration {
   // If given a vector of variables, the selected variables will be part of the
   // result table - the join column will automatically be part of the result.
   // You may use PayloadAllVariables to select all columns of the right table.
-  PayloadVariables payloadVariables_ = PayloadAllVariables{};
+  PayloadVariables payloadVariables_ = PayloadVariables::all();
 
   // Choice of algorithm. Both algorithms have equal results, but different
   // runtime characteristics.

src/parser/CMakeLists.txt

@@ -20,6 +20,7 @@ add_library(parser
         MagicServiceQuery.cpp
         PathQuery.cpp
         SpatialQuery.cpp
+        PayloadVariables.cpp
         PropertyPath.cpp
         data/SparqlFilter.cpp
         SelectClause.cpp

src/parser/PayloadVariables.cpp

@@ -0,0 +1,72 @@
+// Copyright 2024, University of Freiburg,
+// Chair of Algorithms and Data Structures.
+// Author: Christoph Ullinger <[email protected]>
+
+#include "parser/PayloadVariables.h"
+
+// ____________________________________________________________________________
+PayloadVariables::PayloadVariables(std::vector<Variable> variables)
+    : variables_{std::move(variables)} {};
+
+// ____________________________________________________________________________
+PayloadVariables PayloadVariables::all() {
+  PayloadVariables pv{};
+  pv.setToAll();
+  return pv;
+};
+
+// ____________________________________________________________________________
+void PayloadVariables::addVariable(const Variable& variable) {
+  // Helper visitor to check if the payload variables has not been set to all
+  // and a variable can be added. If yes, add it.
+  auto addVarVisitor = [&]<typename T>(T& value) {
+    if constexpr (std::is_same_v<T, std::vector<Variable>>) {
+      value.push_back(variable);
+    }
+  };
+
+  std::visit(addVarVisitor, variables_);
+};
+
+// ____________________________________________________________________________
+void PayloadVariables::setToAll() {
+  variables_ = detail::PayloadAllVariables{};
+};
+
+// ____________________________________________________________________________
+bool PayloadVariables::empty() const {
+  // Helper visitor to check if the payload variables are empty
+  auto emptyVisitor = []<typename T>(const T& value) -> bool {
+    if constexpr (std::is_same_v<T, detail::PayloadAllVariables>) {
+      return false;
+    } else {
+      static_assert(std::is_same_v<T, std::vector<Variable>>);
+      return value.empty();
+    }
+  };
+
+  return std::visit(emptyVisitor, variables_);
+};
+
+// ____________________________________________________________________________
+bool PayloadVariables::isAll() const {
+  return std::holds_alternative<detail::PayloadAllVariables>(variables_);
+};
+
+// ____________________________________________________________________________
+const std::vector<Variable>& PayloadVariables::getVariables() const {
+  // Helper visitor to check if the payload variables has been set to all: then
+  // throw, otherwise return the vector
+  auto getVarVisitor =
+      []<typename T>(const T& value) -> const std::vector<Variable>& {
+    if constexpr (std::is_same_v<T, std::vector<Variable>>) {
+      return value;
+    } else {
+      AD_THROW(
+          "getVariables may only be called on a non-all PayloadVariables "
+          "object.");
+    }
+  };
+
+  return std::visit(getVarVisitor, variables_);
+};

src/parser/PayloadVariables.h

@@ -0,0 +1,57 @@
+// Copyright 2024, University of Freiburg,
+// Chair of Algorithms and Data Structures.
+// Author: Christoph Ullinger <[email protected]>
+
+#pragma once
+
+#include <vector>
+
+#include "parser/data/Variable.h"
+
+namespace detail {
+// Represents the selection of all variables as payload
+struct PayloadAllVariables : std::monostate {
+  bool operator==([[maybe_unused]] const std::vector<Variable>& other) const {
+    return false;
+  };
+};
+}  // namespace detail
+
+// This class represents a list of variables to be included in the result of
+// an operation. This is currently used in the spatial search.
+class PayloadVariables {
+ public:
+  // Construct an empty payload variables object
+  PayloadVariables() = default;
+
+  // Construct a payload variables object from a vector of variables
+  PayloadVariables(std::vector<Variable> variables);
+
+  // Construct a payload variables object that is set to all
+  static PayloadVariables all();
+
+  // Add a variable to the payload variables or do nothing if all variables are
+  // already selected
+  void addVariable(const Variable& variable);
+
+  // Select all variables.
+  void setToAll();
+
+  // Returns whether the payload variables object is empty.
+  bool empty() const;
+
+  // Returns whether all variables have been selected.
+  bool isAll() const;
+
+  // Returns a vector of variables if all has not been set. Otherwise throws.
+  const std::vector<Variable>& getVariables() const;
+
+  // For testing: equality operator
+  bool operator==(const PayloadVariables& other) const {
+    return variables_ == other.variables_;
+  };
+
+ private:
+  std::variant<detail::PayloadAllVariables, std::vector<Variable>> variables_ =
+      std::vector<Variable>{};
+};

src/parser/SpatialQuery.cpp

@@ -4,8 +4,13 @@
 
 #include "parser/SpatialQuery.h"
 
+#include <type_traits>
+#include <variant>
+
 #include "engine/SpatialJoin.h"
 #include "parser/MagicServiceIriConstants.h"
+#include "parser/PayloadVariables.h"
+#include "parser/data/Variable.h"
 
 namespace parsedQuery {
 
@@ -60,7 +65,22 @@ void SpatialQuery::addParameter(const SparqlTriple& triple) {
           "<baseline>, <s2> or <boundingBox>.");
     }
   } else if (predString == "payload") {
-    payloadVariables_.push_back(getVariable("payload", object));
+    if (object.isVariable()) {
+      // Single selected variable
+
+      // If we have already selected all payload variables, we can ignore
+      // another explicitly selected variable.
+      payloadVariables_.addVariable(getVariable("payload", object));
+    } else if (object.isIri() &&
+               extractParameterName(object, SPATIAL_SEARCH_IRI) == "all") {
+      // All variables selected
+      payloadVariables_.setToAll();
+    } else {
+      throw SpatialSearchException(
+          "The argument to the <payload> parameter must be either a variable "
+          "to be selected or <all>.");
+    }
+
   } else {
     throw SpatialSearchException(absl::StrCat(
         "Unsupported argument ", predString,
@@ -95,7 +115,7 @@ SpatialJoinConfiguration SpatialQuery::toSpatialJoinConfiguration() const {
         "spatialSearch: { [Config Triples] { <Something> <ThatSelects> ?right "
         "} }.");
   } else if (!ignoreMissingRightChild_ && !childGraphPattern_.has_value() &&
-             !payloadVariables_.empty()) {
+             !payloadVariables_.isAll() && !payloadVariables_.empty()) {
     throw SpatialSearchException(
         "The right variable for the spatial search is declared outside the "
         "SERVICE, but the <payload> parameter was set. Please move the "
@@ -112,7 +132,7 @@ SpatialJoinConfiguration SpatialQuery::toSpatialJoinConfiguration() const {
   // Payload variables
   PayloadVariables pv;
   if (!childGraphPattern_.has_value()) {
-    pv = PayloadAllVariables{};
+    pv = PayloadVariables::all();
   } else {
     pv = payloadVariables_;
   }

src/parser/SpatialQuery.h

@@ -6,6 +6,7 @@
 
 #include "parser/GraphPattern.h"
 #include "parser/MagicServiceQuery.h"
+#include "parser/PayloadVariables.h"
 
 namespace parsedQuery {
 
@@ -39,7 +40,7 @@ struct SpatialQuery : MagicServiceQuery {
   // this vector is required to be empty - the user may not specify the payload
   // configuration parameter. It will then be automatically set to
   // `PayloadAllVariables` to ensure appropriate semantics.
-  std::vector<Variable> payloadVariables_;
+  PayloadVariables payloadVariables_;
 
   // Optional further argument: the join algorithm. If it is not given, the
   // default algorithm is used implicitly.