From d0fb4d724214ab258a704dd3a0fc2436af243ba7 Mon Sep 17 00:00:00 2001
From: florijan <florijan@memgraph.io>
Date: Fri, 6 Oct 2017 09:33:12 +0200
Subject: [PATCH] BFS - lower bound support
Summary: This is not a very important functionality, but it turned out simple to do, so let's add it to have a consistent query support.
Reviewers: buda, teon.banek
Reviewed By: teon.banek
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D862
---
docs/user_technical/open-cypher.md | 6 ++----
src/query/frontend/ast/cypher_main_visitor.cpp | 2 --
src/query/plan/operator.cpp | 12 ++++++++++--
.../memgraph_V1/features/memgraph_bfs.feature | 17 ++++++++++++++++-
4 files changed, 28 insertions(+), 9 deletions(-)
diff --git a/docs/user_technical/open-cypher.md b/docs/user_technical/open-cypher.md
index 695e04128..373b41cb9 100644
--- a/docs/user_technical/open-cypher.md
+++ b/docs/user_technical/open-cypher.md
@@ -436,10 +436,8 @@ destination node. Furthermore, it's possible to find multiple paths to multiple
nodes regardless of their length. Also, it is possible to simply go through a node's
neighbourhood in breadth-first manner.
-It is fair to say there are a few drawbacks too. Currently, it isn't possible to get
-all shortest paths to a single node using Memgraph's breadth-first expansion. Also
-property maps (in curly brackets) are not supported with a BFS. These features will
-most likely be included in subsequent Memgraph releases.
+Currently, it isn't possible to get all shortest paths to a single node using
+Memgraph's breadth-first expansion.
#### UNWIND
diff --git a/src/query/frontend/ast/cypher_main_visitor.cpp b/src/query/frontend/ast/cypher_main_visitor.cpp
index 8c4aa285e..88ff750ed 100644
--- a/src/query/frontend/ast/cypher_main_visitor.cpp
+++ b/src/query/frontend/ast/cypher_main_visitor.cpp
@@ -570,8 +570,6 @@ antlrcpp::Any CypherMainVisitor::visitVariableExpansion(
upper = ctx->expression()[1]->accept(this);
}
- if (is_bfs && lower)
- throw SemanticException("BFS does not support lower bounds");
return std::make_tuple(is_bfs, lower, upper);
}
diff --git a/src/query/plan/operator.cpp b/src/query/plan/operator.cpp
index b6dea0846..1ece0799d 100644
--- a/src/query/plan/operator.cpp
+++ b/src/query/plan/operator.cpp
@@ -927,6 +927,10 @@ class ExpandBreadthFirstCursor : public query::plan::Cursor {
SwitchAccessor(vertex, self_.graph_view_);
processed_.emplace(vertex, std::experimental::nullopt);
expand_from_vertex(vertex);
+ lower_bound_ = self_.lower_bound_
+ ? EvaluateInt(evaluator, self_.lower_bound_,
+ "Min depth in breadth-first expansion")
+ : 1;
upper_bound_ = self_.upper_bound_
? EvaluateInt(evaluator, self_.upper_bound_,
"Max depth in breadth-first expansion")
@@ -963,6 +967,9 @@ class ExpandBreadthFirstCursor : public query::plan::Cursor {
if (static_cast<int>(edge_list.size()) < upper_bound_)
expand_from_vertex(expansion.second);
+ if (static_cast<int64_t>(edge_list.size()) < lower_bound_)
+ continue;
+
// place destination node on the frame, handle existence flag
if (self_.existing_node_) {
TypedValue &node = frame[self_.node_symbol_];
@@ -990,8 +997,9 @@ class ExpandBreadthFirstCursor : public query::plan::Cursor {
GraphDbAccessor &db_;
const std::unique_ptr<query::plan::Cursor> input_cursor_;
- // maximum depth of the expansion. calculated on each pull
- // from the input, the initial value is irrelevant.
+ // Depth bounds. Calculated on each pull from the input, the initial value is
+ // irrelevant.
+ int lower_bound_{-1};
int upper_bound_{-1};
// maps vertices to the edge they got expanded from. it is an optional
diff --git a/tests/qa/tck_engine/tests/memgraph_V1/features/memgraph_bfs.feature b/tests/qa/tck_engine/tests/memgraph_V1/features/memgraph_bfs.feature
index f6c6a457b..8c4e21607 100644
--- a/tests/qa/tck_engine/tests/memgraph_V1/features/memgraph_bfs.feature
+++ b/tests/qa/tck_engine/tests/memgraph_V1/features/memgraph_bfs.feature
@@ -1,6 +1,6 @@
Feature: Bfs
- Scenario: Test match BFS depth blocked
+ Scenario: Test match BFS upper bound
Given an empty graph
And having executed:
"""
@@ -15,6 +15,21 @@ Feature: Bfs
| '0' | '1.1' |
| '0' | '1.2' |
+ Scenario: Test match BFS lower bound
+ Given an empty graph
+ And having executed:
+ """
+ CREATE (n {a:'0'})-[:r]->({a:'1.1'})-[:r]->({a:'2.1'})-[:r]->({a:'3.1'})
+ """
+ When executing query:
+ """
+ MATCH (n {a:'0'})-[*bfs 2..]->(m) RETURN n.a, m.a
+ """
+ Then the result should be:
+ | n.a | m.a |
+ | '0' | '2.1' |
+ | '0' | '3.1' |
+
Scenario: Test match BFS filtered
Given an empty graph
And having executed: