Implement IS NULL and IS NOT NULL

Reviewers: teon.banek, florijan

Reviewed By: florijan

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D254

src/query/frontend/ast/ast.hpp

@@ -347,6 +347,20 @@ class UnaryMinusOperator : public UnaryOperator {
   using UnaryOperator::UnaryOperator;
 };
 
+class IsNullOperator : public UnaryOperator {
+  friend class AstTreeStorage;
+
+ public:
+  void Accept(TreeVisitorBase &visitor) override {
+    visitor.Visit(*this);
+    expression_->Accept(visitor);
+    visitor.PostVisit(*this);
+  }
+
+ protected:
+  using UnaryOperator::UnaryOperator;
+};
+
 class Literal : public Expression {
   friend class AstTreeStorage;
 

src/query/frontend/ast/ast_visitor.hpp

@@ -29,6 +29,7 @@ class DivisionOperator;
 class ModOperator;
 class UnaryPlusOperator;
 class UnaryMinusOperator;
+class IsNullOperator;
 class NotEqualOperator;
 class EqualOperator;
 class LessOperator;
@@ -48,8 +49,8 @@ using TreeVisitorBase = ::utils::Visitor<
     AdditionOperator, SubtractionOperator, MultiplicationOperator,
     DivisionOperator, ModOperator, NotEqualOperator, EqualOperator,
     LessOperator, GreaterOperator, LessEqualOperator, GreaterEqualOperator,
-    UnaryPlusOperator, UnaryMinusOperator, Identifier, Literal, PropertyLookup,
-    Aggregation, Create, Match, Return, With, Pattern, NodeAtom, EdgeAtom,
-    Delete, Where, SetProperty, SetProperties, SetLabels, RemoveProperty,
-    RemoveLabels>;
+    UnaryPlusOperator, UnaryMinusOperator, IsNullOperator, Identifier, Literal,
+    PropertyLookup, Aggregation, Create, Match, Return, With, Pattern, NodeAtom,
+    EdgeAtom, Delete, Where, SetProperty, SetProperties, SetLabels,
+    RemoveProperty, RemoveLabels>;
 }

src/query/frontend/ast/cypher_main_visitor.cpp

@@ -496,7 +496,21 @@ antlrcpp::Any CypherMainVisitor::visitExpression3(
   // that child is expression2. Other operations are not implemented at the
   // moment.
   // TODO: implement this.
-  if (ctx->children.size() > 1u) {
+  // This is a hack. Unfortunately, grammar for expression3 contains a lot of
+  // different expressions. We should break that production in parts so that
+  // we can easily implement its visitor.
+  Expression *expression = ctx->expression2()[0]->accept(this);
+  if (ctx->children.size() - ctx->SP().size() == 3U && ctx->IS().size() == 1U &&
+      ctx->CYPHERNULL().size() == 1U) {
+    return static_cast<Expression *>(
+        storage_.Create<IsNullOperator>(expression));
+  }
+  if (ctx->children.size() - ctx->SP().size() == 4U && ctx->IS().size() == 1U &&
+      ctx->NOT().size() == 1U && ctx->CYPHERNULL().size() == 1U) {
+    return static_cast<Expression *>(storage_.Create<NotOperator>(
+        storage_.Create<IsNullOperator>(expression)));
+  }
+  if (ctx->children.size() > 1U) {
     throw NotYetImplemented();
   }
   return static_cast<Expression *>(visitChildren(ctx));

src/query/frontend/interpret/interpret.hpp

@@ -105,6 +105,12 @@ class ExpressionEvaluator : public TreeVisitorBase {
   UNARY_OPERATOR_VISITOR(UnaryPlusOperator, +);
   UNARY_OPERATOR_VISITOR(UnaryMinusOperator, -);
 
+  void PostVisit(IsNullOperator &) override {
+    auto expression = PopBack();
+    result_stack_.push_back(
+        TypedValue(expression.type() == TypedValue::Type::Null));
+  }
+
 #undef BINARY_OPERATOR_VISITOR
 #undef UNARY_OPERATOR_VISITOR
 

tests/unit/cypher_main_visitor.cpp

@@ -277,6 +277,30 @@ TEST(CypherMainVisitorTest, ComparisonOperators) {
 
 #undef CHECK_COMPARISON
 
+TEST(CypherMainVisitorTest, IsNull) {
+  AstGenerator ast_generator("RETURN 2 iS NulL");
+  auto *query = ast_generator.query_;
+  auto *return_clause = dynamic_cast<Return *>(query->clauses_[0]);
+  auto *is_type_operator = dynamic_cast<IsNullOperator *>(
+      return_clause->named_expressions_[0]->expression_);
+  auto *operand1 = dynamic_cast<Literal *>(is_type_operator->expression_);
+  ASSERT_TRUE(operand1);
+  ASSERT_EQ(operand1->value_.Value<int64_t>(), 2);
+}
+
+TEST(CypherMainVisitorTest, IsNotNull) {
+  AstGenerator ast_generator("RETURN 2 iS nOT NulL");
+  auto *query = ast_generator.query_;
+  auto *return_clause = dynamic_cast<Return *>(query->clauses_[0]);
+  auto *not_operator = dynamic_cast<NotOperator *>(
+      return_clause->named_expressions_[0]->expression_);
+  auto *is_type_operator =
+      dynamic_cast<IsNullOperator *>(not_operator->expression_);
+  auto *operand1 = dynamic_cast<Literal *>(is_type_operator->expression_);
+  ASSERT_TRUE(operand1);
+  ASSERT_EQ(operand1->value_.Value<int64_t>(), 2);
+}
+
 TEST(CypherMainVisitorTest, NotOperator) {
   AstGenerator ast_generator("RETURN not true");
   auto *query = ast_generator.query_;

tests/unit/query_expression_evaluator.cpp

@@ -232,3 +232,15 @@ TEST(ExpressionEvaluator, UnaryMinusOperator) {
   op->Accept(eval.eval);
   ASSERT_EQ(eval.eval.PopBack().Value<int64_t>(), -5);
 }
+
+TEST(ExpressionEvaluator, IsNullOperator) {
+  AstTreeStorage storage;
+  NoContextExpressionEvaluator eval;
+  auto *op = storage.Create<IsNullOperator>(storage.Create<Literal>(1));
+  op->Accept(eval.eval);
+  ASSERT_EQ(eval.eval.PopBack().Value<bool>(), false);
+  op =
+      storage.Create<IsNullOperator>(storage.Create<Literal>(TypedValue::Null));
+  op->Accept(eval.eval);
+  ASSERT_EQ(eval.eval.PopBack().Value<bool>(), true);
+}