Counter function added

Reviewers: buda, mferencevic, mislav.bradac

Reviewed By: mislav.bradac

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D787

CHANGELOG.md

@@ -11,6 +11,7 @@
 * Map indexing supported.
 * `assert` function added.
 * Use \u to specify 4 digit codepoint and \U for 8 digit
+* `counter` function added.
 
 ### Bug Fixes and Other Changes
 

docs/user_technical/open-cypher.md

@@ -500,6 +500,7 @@ functions.
  `contains`   | Check if the first argument has an element which is equal to the second argument.
  `all`        | Check if all elements of a list satisfy a predicate.<br/>The syntax is: `all(variable IN list WHERE predicate)`.
  `assert`     | Raises an exception reported to the client if the given argument is not `true`.
+ `counter`    | Generates integers that are guaranteed to be unique on the database level, for the given counter name.
 
 #### String Operators
 

src/database/graph_db.hpp

@@ -5,6 +5,7 @@
 #include "cppitertools/filter.hpp"
 #include "cppitertools/imap.hpp"
 
+#include "data_structures/concurrent/concurrent_map.hpp"
 #include "data_structures/concurrent/concurrent_set.hpp"
 #include "data_structures/concurrent/skiplist.hpp"
 #include "database/graph_db_datatypes.hpp"
@@ -120,4 +121,7 @@ class GraphDb {
   // Periodically wakes up and hints to transactions that are running for a long
   // time to stop their execution.
   Scheduler transaction_killer_;
+
+  // DB level global counters, used in the "counter" function
+  ConcurrentMap<std::string, std::atomic<int64_t>> counters_;
 };

src/database/graph_db_accessor.cpp

@@ -328,3 +328,9 @@ const std::string &GraphDbAccessor::PropertyName(
   debug_assert(!commited_ && !aborted_, "Accessor committed or aborted");
   return *property;
 }
+
+int64_t GraphDbAccessor::Counter(const std::string &name) {
+  return db_.counters_.access()
+      .emplace(name, std::make_tuple(name), std::make_tuple(0))
+      .first->second.fetch_add(1);
+}

src/database/graph_db_accessor.hpp

@@ -561,6 +561,13 @@ class GraphDbAccessor {
     if (!accessor.new_) accessor.new_ = accessor.vlist_->update(*transaction_);
   }
 
+  /**
+   * Returns the current value of the counter with the given name, and
+   * increments that counter. If the counter with the given name does not exist,
+   * a new counter is created and this function returns 0.
+   */
+  int64_t Counter(const std::string &name);
+
  private:
   /**
    * Insert this vertex into corresponding label and label+property (if it

src/query/interpret/awesome_memgraph_functions.cpp

@@ -512,18 +512,27 @@ TypedValue Assert(const std::vector<TypedValue> &args, GraphDbAccessor &) {
     throw QueryRuntimeException("assert takes one or two arguments");
   }
   if (args[0].type() != TypedValue::Type::Bool)
-      throw QueryRuntimeException("first assert argument must be bool");
+    throw QueryRuntimeException("first assert argument must be bool");
   if (args.size() == 2U && args[1].type() != TypedValue::Type::String)
-      throw QueryRuntimeException("second assert argument must be a string");
+    throw QueryRuntimeException("second assert argument must be a string");
   if (!args[0].ValueBool()) {
     std::string message("assertion failed");
-    if (args.size() == 2U)
-      message += ": " + args[1].ValueString();
+    if (args.size() == 2U) message += ": " + args[1].ValueString();
     throw QueryRuntimeException(message);
   }
   return args[0];
 }
-} // annonymous namespace
+
+TypedValue Counter(const std::vector<TypedValue> &args, GraphDbAccessor &dba) {
+  if (args.size() != 1U) {
+    throw QueryRuntimeException("counter takes one argument");
+  }
+  if (!args[0].IsString())
+    throw QueryRuntimeException("first counter argument must be a string");
+
+  return dba.Counter(args[0].ValueString());
+}
+}  // annonymous namespace
 
 std::function<TypedValue(const std::vector<TypedValue> &, GraphDbAccessor &)>
 NameToFunction(const std::string &function_name) {
@@ -566,6 +575,7 @@ NameToFunction(const std::string &function_name) {
   if (function_name == kEndsWith) return EndsWith;
   if (function_name == kContains) return Contains;
   if (function_name == "ASSERT") return Assert;
+  if (function_name == "COUNTER") return Counter;
   return nullptr;
 }
-} // namespace query
+}  // namespace query

tests/qa/tck_engine/tests/memgraph_V1/features/functions.feature

@@ -690,3 +690,20 @@ Feature: Functions
         Then the result should be:
             | res  |
             | true |
+
+    Scenario: Counter test:
+        Given an empty graph
+        And having executed:
+            """
+            CREATE (), (), ()
+            """
+        When executing query:
+            """
+            MATCH (n) SET n.id = counter("n.id") WITH n SKIP 1
+            RETURN n.id, counter("other") AS c2
+            """
+        Then the result should be:
+            | n.id | c2 |
+            | 1    | 0  |
+            | 2    | 1  |
+

tests/unit/query_expression_evaluator.cpp

@@ -36,11 +36,13 @@ struct NoContextExpressionEvaluator {
 };
 
 TypedValue EvaluateFunction(const std::string &function_name,
-                            const std::vector<TypedValue> &args) {
+                            const std::vector<TypedValue> &args, Dbms &dbms) {
   AstTreeStorage storage;
-  NoContextExpressionEvaluator eval;
-  Dbms dbms;
+  SymbolTable symbol_table;
   auto dba = dbms.active();
+  Frame frame{128};
+  Parameters parameters;
+  ExpressionEvaluator eval{frame, parameters, symbol_table, *dba};
 
   std::vector<Expression *> expressions;
   for (const auto &arg : args) {
@@ -48,7 +50,13 @@ TypedValue EvaluateFunction(const std::string &function_name,
   }
   auto *op =
       storage.Create<Function>(NameToFunction(function_name), expressions);
-  return op->Accept(eval.eval);
+  return op->Accept(eval);
+}
+
+TypedValue EvaluateFunction(const std::string &function_name,
+                            const std::vector<TypedValue> &args) {
+  Dbms dbms;
+  return EvaluateFunction(function_name, args, dbms);
 }
 
 TEST(ExpressionEvaluator, OrOperator) {
@@ -1166,13 +1174,17 @@ TEST(ExpressionEvaluator, FunctionAllWhereWrongType) {
 TEST(ExpressionEvaluator, FunctionAssert) {
   // Invalid calls.
   ASSERT_THROW(EvaluateFunction("ASSERT", {}), QueryRuntimeException);
-  ASSERT_THROW(EvaluateFunction("ASSERT", {false, false}), QueryRuntimeException);
-  ASSERT_THROW(EvaluateFunction("ASSERT", {"string", false}), QueryRuntimeException);
-  ASSERT_THROW(EvaluateFunction("ASSERT", {false, "reason", true}), QueryRuntimeException);
+  ASSERT_THROW(EvaluateFunction("ASSERT", {false, false}),
+               QueryRuntimeException);
+  ASSERT_THROW(EvaluateFunction("ASSERT", {"string", false}),
+               QueryRuntimeException);
+  ASSERT_THROW(EvaluateFunction("ASSERT", {false, "reason", true}),
+               QueryRuntimeException);
 
   // Valid calls, assertion fails.
   ASSERT_THROW(EvaluateFunction("ASSERT", {false}), QueryRuntimeException);
-  ASSERT_THROW(EvaluateFunction("ASSERT", {false, "message"}), QueryRuntimeException);
+  ASSERT_THROW(EvaluateFunction("ASSERT", {false, "message"}),
+               QueryRuntimeException);
   try {
     EvaluateFunction("ASSERT", {false, "bbgba"});
   } catch (QueryRuntimeException &e) {
@@ -1194,4 +1206,16 @@ TEST(ExpressionEvaluator, ParameterLookup) {
   EXPECT_EQ(value.Value<int64_t>(), 42);
 }
 
+TEST(ExpressionEvaluator, FunctionCounter) {
+  Dbms dbms;
+  EXPECT_THROW(EvaluateFunction("COUNTER", {}, dbms), QueryRuntimeException);
+  EXPECT_THROW(EvaluateFunction("COUNTER", {"a", "b"}, dbms),
+               QueryRuntimeException);
+  EXPECT_EQ(EvaluateFunction("COUNTER", {"c1"}, dbms).ValueInt(), 0);
+  EXPECT_EQ(EvaluateFunction("COUNTER", {"c1"}, dbms).ValueInt(), 1);
+  EXPECT_EQ(EvaluateFunction("COUNTER", {"c2"}, dbms).ValueInt(), 0);
+  EXPECT_EQ(EvaluateFunction("COUNTER", {"c1"}, dbms).ValueInt(), 2);
+  EXPECT_EQ(EvaluateFunction("COUNTER", {"c2"}, dbms).ValueInt(), 1);
+}
+
 }  // namespace