Add BreadthFirstAtom to Ast

Summary: Add BFS to Cypher grammar

Reviewers: florijan, mislav.bradac

Reviewed By: mislav.bradac

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D605

src/query/frontend/ast/ast.hpp

@@ -878,8 +878,10 @@ class EdgeAtom : public PatternAtom {
       edge_atom->properties_[property.first] = property.second->Clone(storage);
     }
     edge_atom->has_range_ = has_range_;
-    edge_atom->lower_bound_ = lower_bound_ ? lower_bound_->Clone(storage) : nullptr;
-    edge_atom->upper_bound_ = upper_bound_ ? upper_bound_->Clone(storage) : nullptr;
+    edge_atom->lower_bound_ =
+        lower_bound_ ? lower_bound_->Clone(storage) : nullptr;
+    edge_atom->upper_bound_ =
+        upper_bound_ ? upper_bound_->Clone(storage) : nullptr;
     return edge_atom;
   }
 
@@ -897,6 +899,49 @@ class EdgeAtom : public PatternAtom {
       : PatternAtom(uid, identifier), direction_(direction) {}
 };
 
+class BreadthFirstAtom : public EdgeAtom {
+  // TODO: Reconsider inheriting from EdgeAtom, since only `direction_` is used.
+  friend class AstTreeStorage;
+
+ public:
+  DEFVISITABLE(TreeVisitor<TypedValue>);
+  bool Accept(HierarchicalTreeVisitor &visitor) override {
+    if (visitor.PreVisit(*this)) {
+      identifier_->Accept(visitor) &&
+          traversed_edge_identifier_->Accept(visitor) &&
+          next_node_identifier_->Accept(visitor) &&
+          filter_expression_->Accept(visitor) && max_depth_->Accept(visitor);
+    }
+    return visitor.PostVisit(*this);
+  }
+
+  BreadthFirstAtom *Clone(AstTreeStorage &storage) const override {
+    return storage.Create<BreadthFirstAtom>(
+        identifier_->Clone(storage), direction_,
+        traversed_edge_identifier_->Clone(storage),
+        next_node_identifier_->Clone(storage),
+        filter_expression_->Clone(storage), max_depth_->Clone(storage));
+  }
+
+  Identifier *traversed_edge_identifier_ = nullptr;
+  Identifier *next_node_identifier_ = nullptr;
+  // Expression which evaluates to true in order to continue the BFS.
+  Expression *filter_expression_ = nullptr;
+  Expression *max_depth_ = nullptr;
+
+ protected:
+  using EdgeAtom::EdgeAtom;
+  BreadthFirstAtom(int uid, Identifier *identifier, Direction direction,
+                   Identifier *traversed_edge_identifier,
+                   Identifier *next_node_identifier,
+                   Expression *filter_expression, Expression *max_depth)
+      : EdgeAtom(uid, identifier, direction),
+        traversed_edge_identifier_(traversed_edge_identifier),
+        next_node_identifier_(next_node_identifier),
+        filter_expression_(filter_expression),
+        max_depth_(max_depth) {}
+};
+
 class Clause : public Tree {
   friend class AstTreeStorage;
 

src/query/frontend/ast/ast_visitor.hpp

@@ -21,6 +21,7 @@ class With;
 class Pattern;
 class NodeAtom;
 class EdgeAtom;
+class BreadthFirstAtom;
 class PrimitiveLiteral;
 class ListLiteral;
 class OrOperator;
@@ -65,8 +66,8 @@ using TreeCompositeVisitor = ::utils::CompositeVisitor<
     ListSlicingOperator, UnaryPlusOperator, UnaryMinusOperator, IsNullOperator,
     ListLiteral, PropertyLookup, LabelsTest, EdgeTypeTest, Aggregation,
     Function, All, Create, Match, Return, With, Pattern, NodeAtom, EdgeAtom,
-    Delete, Where, SetProperty, SetProperties, SetLabels, RemoveProperty,
-    RemoveLabels, Merge, Unwind>;
+    BreadthFirstAtom, Delete, Where, SetProperty, SetProperties, SetLabels,
+    RemoveProperty, RemoveLabels, Merge, Unwind>;
 
 using TreeLeafVisitor =
     ::utils::LeafVisitor<Identifier, PrimitiveLiteral, CreateIndex>;
@@ -90,7 +91,8 @@ using TreeVisitor = ::utils::Visitor<
     ListSlicingOperator, UnaryPlusOperator, UnaryMinusOperator, IsNullOperator,
     ListLiteral, PropertyLookup, LabelsTest, EdgeTypeTest, Aggregation,
     Function, All, Create, Match, Return, With, Pattern, NodeAtom, EdgeAtom,
-    Delete, Where, SetProperty, SetProperties, SetLabels, RemoveProperty,
-    RemoveLabels, Merge, Unwind, Identifier, PrimitiveLiteral, CreateIndex>;
+    BreadthFirstAtom, Delete, Where, SetProperty, SetProperties, SetLabels,
+    RemoveProperty, RemoveLabels, Merge, Unwind, Identifier, PrimitiveLiteral,
+    CreateIndex>;
 
 }  // namespace query

src/query/frontend/ast/cypher_main_visitor.cpp

@@ -413,8 +413,26 @@ antlrcpp::Any CypherMainVisitor::visitPatternElementChain(
 
 antlrcpp::Any CypherMainVisitor::visitRelationshipPattern(
     CypherParser::RelationshipPatternContext *ctx) {
-  auto *edge = storage_.Create<EdgeAtom>();
-  if (ctx->relationshipDetail()) {
+  auto *edge = ctx->bfsDetail() ? storage_.Create<BreadthFirstAtom>()
+                                : storage_.Create<EdgeAtom>();
+  if (ctx->bfsDetail()) {
+    if (ctx->bfsDetail()->bfs_variable) {
+      std::string variable = ctx->bfsDetail()->bfs_variable->accept(this);
+      edge->identifier_ = storage_.Create<Identifier>(variable);
+      users_identifiers.insert(variable);
+    }
+    auto *bf_atom = dynamic_cast<BreadthFirstAtom *>(edge);
+    std::string traversed_edge_variable =
+        ctx->bfsDetail()->traversed_edge->accept(this);
+    bf_atom->traversed_edge_identifier_ =
+        storage_.Create<Identifier>(traversed_edge_variable);
+    std::string next_node_variable = ctx->bfsDetail()->next_node->accept(this);
+    bf_atom->next_node_identifier_ =
+        storage_.Create<Identifier>(next_node_variable);
+    bf_atom->filter_expression_ =
+        ctx->bfsDetail()->expression()[0]->accept(this);
+    bf_atom->max_depth_ = ctx->bfsDetail()->expression()[1]->accept(this);
+  } else if (ctx->relationshipDetail()) {
     if (ctx->relationshipDetail()->variable()) {
       std::string variable =
           ctx->relationshipDetail()->variable()->accept(this);
@@ -466,6 +484,12 @@ antlrcpp::Any CypherMainVisitor::visitRelationshipDetail(
   return 0;
 }
 
+antlrcpp::Any CypherMainVisitor::visitBfsDetail(
+    CypherParser::BfsDetailContext *) {
+  debug_assert(false, "Should never be called. See documentation in hpp.");
+  return 0;
+}
+
 antlrcpp::Any CypherMainVisitor::visitRelationshipTypes(
     CypherParser::RelationshipTypesContext *ctx) {
   std::vector<GraphDbTypes::EdgeType> types;

src/query/frontend/ast/cypher_main_visitor.hpp

@@ -268,6 +268,12 @@ class CypherMainVisitor : public antlropencypher::CypherBaseVisitor {
   antlrcpp::Any visitRelationshipDetail(
       CypherParser::RelationshipDetailContext *ctx) override;
 
+  /**
+   * This should never be called. Everything is done directly in
+   * visitRelationshipPattern.
+   */
+  antlrcpp::Any visitBfsDetail(CypherParser::BfsDetailContext *ctx) override;
+
   /**
    * @return vector<GraphDbTypes::EdgeType>
    */

src/query/frontend/opencypher/grammar/Cypher.g4

@@ -110,12 +110,14 @@ nodePattern : '(' SP? ( variable SP? )? ( nodeLabels SP? )? ( properties SP? )?
 
 patternElementChain : relationshipPattern SP? nodePattern ;
 
-relationshipPattern : ( leftArrowHead SP? dash SP? relationshipDetail? SP? dash SP? rightArrowHead )
-                    | ( leftArrowHead SP? dash SP? relationshipDetail? SP? dash )
-                    | ( dash SP? relationshipDetail? SP? dash SP? rightArrowHead )
-                    | ( dash SP? relationshipDetail? SP? dash )
+relationshipPattern : ( leftArrowHead SP? dash SP? ( bfsDetail | relationshipDetail )? SP? dash SP? rightArrowHead )
+                    | ( leftArrowHead SP? dash SP? ( bfsDetail | relationshipDetail )? SP? dash )
+                    | ( dash SP? ( bfsDetail | relationshipDetail )? SP? dash SP? rightArrowHead )
+                    | ( dash SP? ( bfsDetail | relationshipDetail )? SP? dash )
                     ;
 
+bfsDetail : BFS SP? ( '[' SP? ( bfs_variable=variable SP? )? ']' )? SP? '(' SP? traversed_edge=variable SP? ',' SP? next_node=variable SP? '|' SP? expression SP? ',' SP? expression SP? ')' ;
+
 relationshipDetail : '[' SP? ( variable SP? )? ( relationshipTypes SP? )? ( rangeLiteral SP? )? properties SP? ']'
                    | '[' SP? ( variable SP? )? ( relationshipTypes SP? )? ( rangeLiteral SP? )? ( properties SP? )? ']'
                    ;
@@ -445,6 +447,8 @@ FALSE : ( 'F' | 'f' ) ( 'A' | 'a' ) ( 'L' | 'l' ) ( 'S' | 's' ) ( 'E' | 'e' )  ;
 
 INDEX : ( 'I' | 'i') ( 'N' | 'n' ) ( 'D' | 'd' ) ( 'E' | 'e' ) ( 'X' | 'x' ) ;
 
+BFS : ( 'B' | 'b' ) ( 'F' | 'f' ) ( 'S' | 's' ) ;
+
 UnescapedSymbolicName : IdentifierStart ( IdentifierPart )* ;
 
 /**

src/query/interpret/eval.hpp

@@ -42,6 +42,7 @@ class ExpressionEvaluator : public TreeVisitor<TypedValue> {
   BLOCK_VISIT(Pattern);
   BLOCK_VISIT(NodeAtom);
   BLOCK_VISIT(EdgeAtom);
+  BLOCK_VISIT(BreadthFirstAtom);
   BLOCK_VISIT(Delete);
   BLOCK_VISIT(Where);
   BLOCK_VISIT(SetProperty);

tests/unit/cypher_main_visitor.cpp

@@ -1400,4 +1400,26 @@ TYPED_TEST(CypherMainVisitorTest, ReturnAll) {
   EXPECT_TRUE(eq);
 }
 
+TYPED_TEST(CypherMainVisitorTest, MatchBfsReturn) {
+  TypeParam ast_generator(
+      "MATCH (n) -bfs[r](e, n|e.prop = 42, 10)-> (m) RETURN r");
+  auto *query = ast_generator.query_;
+  ASSERT_EQ(query->clauses_.size(), 2U);
+  auto *match = dynamic_cast<Match *>(query->clauses_[0]);
+  ASSERT_TRUE(match);
+  ASSERT_EQ(match->patterns_.size(), 1U);
+  ASSERT_EQ(match->patterns_[0]->atoms_.size(), 3U);
+  auto *bfs = dynamic_cast<BreadthFirstAtom *>(match->patterns_[0]->atoms_[1]);
+  ASSERT_TRUE(bfs);
+  EXPECT_EQ(bfs->direction_, EdgeAtom::Direction::OUT);
+  EXPECT_EQ(bfs->identifier_->name_, "r");
+  EXPECT_EQ(bfs->traversed_edge_identifier_->name_, "e");
+  EXPECT_EQ(bfs->next_node_identifier_->name_, "n");
+  auto *max_depth = dynamic_cast<PrimitiveLiteral *>(bfs->max_depth_);
+  ASSERT_TRUE(max_depth);
+  EXPECT_EQ(max_depth->value_.Value<int64_t>(), 10U);
+  auto *eq = dynamic_cast<EqualOperator *>(bfs->filter_expression_);
+  ASSERT_TRUE(eq);
+}
+
 }