EdgeAccessor::is_cycle added. Query::Plan::Expand fixed

Reviewers: mislav.bradac

Reviewed By: mislav.bradac

Differential Revision: https://phabricator.memgraph.io/D262

src/query/frontend/logical/operator.cpp

@@ -242,6 +242,12 @@ bool Expand::ExpandCursor::Pull(Frame &frame, const SymbolTable &symbol_table) {
     // attempt to get a value from the outgoing edges
     if (out_edges_ && *out_edges_it_ != out_edges_->end()) {
       EdgeAccessor edge = *(*out_edges_it_)++;
+      // when expanding in EdgeAtom::Direction::BOTH directions
+      // we should do only one expansion for cycles, and it was
+      // already done in the block above
+      if (self_.edge_atom_->direction_ == EdgeAtom::Direction::BOTH &&
+          edge.is_cycle())
+        continue;
       if (HandleEdgeCycle(edge, frame, symbol_table) &&
           PullNode(edge, EdgeAtom::Direction::RIGHT, frame, symbol_table))
         return true;

src/storage/edge_accessor.cpp

@@ -15,6 +15,9 @@ VertexAccessor EdgeAccessor::from() const {
 VertexAccessor EdgeAccessor::to() const {
   return VertexAccessor(current().to_, db_accessor());
 }
+bool EdgeAccessor::is_cycle() const {
+  return &current().to_ == &current().from_;
+}
 
 std::ostream &operator<<(std::ostream &os, const EdgeAccessor &ea) {
   os << "E[" << ea.db_accessor().edge_type_name(ea.edge_type());

src/storage/edge_accessor.hpp

@@ -38,7 +38,9 @@ class EdgeAccessor : public RecordAccessor<Edge> {
    */
   VertexAccessor to() const;
 
-  //  void remove();
+  /** Returns true if this edge is a cycle (start and end node are
+   * the same. */
+  bool is_cycle() const;
 };
 
 std::ostream &operator<<(std::ostream &, const EdgeAccessor &);

tests/unit/query_plan_match_filter_return.cpp

@@ -314,6 +314,25 @@ TEST(QueryPlan, ExpandEdgeCycle) {
   test_cycle(false, 6);
 }
 
+TEST(QueryPlan, ExpandBothCycleEdgeCase) {
+  // we're testing that expanding on BOTH
+  // does only one expansion for a cycle
+  Dbms dbms;
+  auto dba = dbms.active();
+
+  auto v = dba->insert_vertex();
+  dba->insert_edge(v, v, dba->edge_type("et"));
+  dba->advance_command();
+
+  AstTreeStorage storage;
+  SymbolTable symbol_table;
+
+  auto n = MakeScanAll(storage, symbol_table, "n");
+  auto r_ = MakeExpand(storage, symbol_table, n.op_, n.sym_, "r",
+                       EdgeAtom::Direction::BOTH, false, "_", false);
+  EXPECT_EQ(1, PullAll(r_.op_, *dba, symbol_table));
+}
+
 TEST(QueryPlan, EdgeFilter) {
   Dbms dbms;
   auto dba = dbms.active();

tests/unit/record_edge_vertex_accessor.cpp

@@ -202,6 +202,19 @@ TEST(RecordAccessor, EdgeType) {
   EXPECT_NE(edge.edge_type(), hates);
 }
 
+TEST(RecordAccessor, EdgeIsCycle) {
+  Dbms dbms;
+  auto dba = dbms.active();
+  auto v1 = dba->insert_vertex();
+  auto v2 = dba->insert_vertex();
+  auto likes = dba->edge_type("edge_type");
+
+  EXPECT_TRUE(dba->insert_edge(v1, v1, likes).is_cycle());
+  EXPECT_TRUE(dba->insert_edge(v2, v2, likes).is_cycle());
+  EXPECT_FALSE(dba->insert_edge(v1, v2, likes).is_cycle());
+  EXPECT_FALSE(dba->insert_edge(v2, v1, likes).is_cycle());
+}
+
 TEST(RecordAccessor, VertexEdgeConnections) {
   Dbms dbms;
   auto dba = dbms.active();