Add command NULLIF for identifying nulls in LOAD CSV (#914)

Add NULLIF command which turns all row values corresponding to the string to the nullif character sequence.

src/query/frontend/ast/ast.hpp

@@ -3022,6 +3022,7 @@ class LoadCsv : public memgraph::query::Clause {
   bool ignore_bad_;
   memgraph::query::Expression *delimiter_{nullptr};
   memgraph::query::Expression *quote_{nullptr};
+  memgraph::query::Expression *nullif_{nullptr};
   memgraph::query::Identifier *row_var_{nullptr};
 
   LoadCsv *Clone(AstStorage *storage) const override {
@@ -3031,18 +3032,20 @@ class LoadCsv : public memgraph::query::Clause {
     object->ignore_bad_ = ignore_bad_;
     object->delimiter_ = delimiter_ ? delimiter_->Clone(storage) : nullptr;
     object->quote_ = quote_ ? quote_->Clone(storage) : nullptr;
+    object->nullif_ = nullif_;
     object->row_var_ = row_var_ ? row_var_->Clone(storage) : nullptr;
     return object;
   }
 
  protected:
   explicit LoadCsv(Expression *file, bool with_header, bool ignore_bad, Expression *delimiter, Expression *quote,
-                   Identifier *row_var)
+                   Expression *nullif, Identifier *row_var)
       : file_(file),
         with_header_(with_header),
         ignore_bad_(ignore_bad),
         delimiter_(delimiter),
         quote_(quote),
+        nullif_(nullif),
         row_var_(row_var) {
     DMG_ASSERT(row_var, "LoadCsv cannot take nullptr for identifier");
   }

src/query/frontend/ast/cypher_main_visitor.cpp

@@ -362,6 +362,11 @@ antlrcpp::Any CypherMainVisitor::visitLoadCsv(MemgraphCypher::LoadCsvContext *ct
   // handle skip bad row option
   load_csv->ignore_bad_ = ctx->IGNORE() && ctx->BAD();
 
+  // handle character sequence which will correspond to nulls
+  if (ctx->NULLIF()) {
+    load_csv->nullif_ = std::any_cast<Expression *>(ctx->nullif()->accept(this));
+  }
+
   // handle delimiter
   if (ctx->DELIMITER()) {
     if (ctx->delimiter()->literal()->StringLiteral()) {

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

@@ -59,6 +59,7 @@ memgraphCypherKeyword : cypherKeyword
                       | GRANT
                       | HEADER
                       | IDENTIFIED
+                      | NULLIF
                       | ISOLATION
                       | IN_MEMORY_ANALYTICAL
                       | IN_MEMORY_TRANSACTIONAL
@@ -224,6 +225,7 @@ loadCsv : LOAD CSV FROM csvFile ( WITH | NO ) HEADER
          ( IGNORE BAD ) ?
          ( DELIMITER delimiter ) ?
          ( QUOTE quote ) ?
+         ( NULLIF nullif ) ?
          AS rowVar ;
 
 csvFile : literal ;
@@ -232,6 +234,8 @@ delimiter : literal ;
 
 quote : literal ;
 
+nullif : literal ;
+
 rowVar : variable ;
 
 userOrRoleName : symbolicName ;

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

@@ -85,6 +85,7 @@ MODULE_WRITE            : M O D U L E UNDERSCORE W R I T E ;
 NEXT                    : N E X T ;
 NO                      : N O ;
 NOTHING                 : N O T H I N G ;
+NULLIF                  : N U L L I F ;
 PASSWORD                : P A S S W O R D ;
 PORT                    : P O R T ;
 PRIVILEGES              : P R I V I L E G E S ;

src/query/plan/operator.cpp

@@ -4637,13 +4637,14 @@ UniqueCursorPtr CallProcedure::MakeCursor(utils::MemoryResource *mem) const {
 }
 
 LoadCsv::LoadCsv(std::shared_ptr<LogicalOperator> input, Expression *file, bool with_header, bool ignore_bad,
-                 Expression *delimiter, Expression *quote, Symbol row_var)
+                 Expression *delimiter, Expression *quote, Expression *nullif, Symbol row_var)
     : input_(input ? input : (std::make_shared<Once>())),
       file_(file),
       with_header_(with_header),
       ignore_bad_(ignore_bad),
       delimiter_(delimiter),
       quote_(quote),
+      nullif_(nullif),
       row_var_(row_var) {
   MG_ASSERT(file_, "Something went wrong - '{}' member file_ shouldn't be a nullptr", __func__);
 }
@@ -4674,22 +4675,31 @@ auto ToOptionalString(ExpressionEvaluator *evaluator, Expression *expression) ->
   return std::nullopt;
 };
 
-TypedValue CsvRowToTypedList(csv::Reader::Row &row) {
+TypedValue CsvRowToTypedList(csv::Reader::Row &row, std::optional<utils::pmr::string> &nullif) {
   auto *mem = row.get_allocator().GetMemoryResource();
   auto typed_columns = utils::pmr::vector<TypedValue>(mem);
   typed_columns.reserve(row.size());
   for (auto &column : row) {
-    typed_columns.emplace_back(std::move(column));
+    if (!nullif.has_value() || column != nullif.value()) {
+      typed_columns.emplace_back(std::move(column));
+    } else {
+      typed_columns.emplace_back();
+    }
   }
   return {std::move(typed_columns), mem};
 }
 
-TypedValue CsvRowToTypedMap(csv::Reader::Row &row, csv::Reader::Header header) {
+TypedValue CsvRowToTypedMap(csv::Reader::Row &row, csv::Reader::Header header,
+                            std::optional<utils::pmr::string> &nullif) {
   // a valid row has the same number of elements as the header
   auto *mem = row.get_allocator().GetMemoryResource();
   utils::pmr::map<utils::pmr::string, TypedValue> m(mem);
   for (auto i = 0; i < row.size(); ++i) {
-    m.emplace(std::move(header[i]), std::move(row[i]));
+    if (!nullif.has_value() || row[i] != nullif.value()) {
+      m.emplace(std::move(header[i]), std::move(row[i]));
+    } else {
+      m.emplace(std::piecewise_construct, std::forward_as_tuple(std::move(header[i])), std::forward_as_tuple());
+    }
   }
   return {std::move(m), mem};
 }
@@ -4701,6 +4711,7 @@ class LoadCsvCursor : public Cursor {
   const UniqueCursorPtr input_cursor_;
   bool did_pull_;
   std::optional<csv::Reader> reader_{};
+  std::optional<utils::pmr::string> nullif_;
 
  public:
   LoadCsvCursor(const LoadCsv *self, utils::MemoryResource *mem)
@@ -4718,6 +4729,7 @@ class LoadCsvCursor : public Cursor {
     //  without massacring the code even worse than I did here
     if (UNLIKELY(!reader_)) {
       reader_ = MakeReader(&context.evaluation_context);
+      nullif_ = ParseNullif(&context.evaluation_context);
     }
 
     if (input_cursor_->Pull(frame, context)) {
@@ -4733,10 +4745,10 @@ class LoadCsvCursor : public Cursor {
       return false;
     }
     if (!reader_->HasHeader()) {
-      frame[self_->row_var_] = CsvRowToTypedList(*row);
+      frame[self_->row_var_] = CsvRowToTypedList(*row, nullif_);
     } else {
       frame[self_->row_var_] =
-          CsvRowToTypedMap(*row, csv::Reader::Header(reader_->GetHeader(), context.evaluation_context.memory));
+          CsvRowToTypedMap(*row, csv::Reader::Header(reader_->GetHeader(), context.evaluation_context.memory), nullif_);
     }
     if (context.frame_change_collector && context.frame_change_collector->IsKeyTracked(self_->row_var_.name())) {
       context.frame_change_collector->ResetTrackingValue(self_->row_var_.name());
@@ -4768,6 +4780,15 @@ class LoadCsvCursor : public Cursor {
         csv::Reader::Config(self_->with_header_, self_->ignore_bad_, std::move(maybe_delim), std::move(maybe_quote)),
         utils::NewDeleteResource());
   }
+
+  std::optional<utils::pmr::string> ParseNullif(EvaluationContext *eval_context) {
+    Frame frame(0);
+    SymbolTable symbol_table;
+    DbAccessor *dba = nullptr;
+    auto evaluator = ExpressionEvaluator(&frame, symbol_table, *eval_context, dba, storage::View::OLD);
+
+    return ToOptionalString(&evaluator, self_->nullif_);
+  }
 };
 
 UniqueCursorPtr LoadCsv::MakeCursor(utils::MemoryResource *mem) const {

src/query/plan/operator.hpp

@@ -2227,7 +2227,7 @@ class LoadCsv : public memgraph::query::plan::LogicalOperator {
 
   LoadCsv() = default;
   LoadCsv(std::shared_ptr<LogicalOperator> input, Expression *file, bool with_header, bool ignore_bad,
-          Expression *delimiter, Expression *quote, Symbol row_var);
+          Expression *delimiter, Expression *quote, Expression *nullif, Symbol row_var);
   bool Accept(HierarchicalLogicalOperatorVisitor &visitor) override;
   UniqueCursorPtr MakeCursor(utils::MemoryResource *) const override;
   std::vector<Symbol> OutputSymbols(const SymbolTable &) const override;
@@ -2243,6 +2243,7 @@ class LoadCsv : public memgraph::query::plan::LogicalOperator {
   bool ignore_bad_;
   Expression *delimiter_{nullptr};
   Expression *quote_{nullptr};
+  Expression *nullif_{nullptr};
   Symbol row_var_;
 
   std::unique_ptr<LogicalOperator> Clone(AstStorage *storage) const override {
@@ -2253,6 +2254,7 @@ class LoadCsv : public memgraph::query::plan::LogicalOperator {
     object->ignore_bad_ = ignore_bad_;
     object->delimiter_ = delimiter_ ? delimiter_->Clone(storage) : nullptr;
     object->quote_ = quote_ ? quote_->Clone(storage) : nullptr;
+    object->nullif_ = nullif_;
     object->row_var_ = row_var_;
     return object;
   }

src/query/plan/pretty_print.cpp

@@ -895,6 +895,10 @@ bool PlanToJsonVisitor::PreVisit(query::plan::LoadCsv &op) {
     self["quote"] = ToJson(op.quote_);
   }
 
+  if (op.nullif_) {
+    self["nullif"] = ToJson(op.nullif_);
+  }
+
   self["row_variable"] = ToJson(op.row_var_);
 
   op.input_->Accept(*this);

src/query/plan/rule_based_planner.hpp

@@ -226,10 +226,9 @@ class RuleBasedPlanner {
             const auto &row_sym = context.symbol_table->at(*load_csv->row_var_);
             context.bound_symbols.insert(row_sym);
 
-            input_op =
-                std::make_unique<plan::LoadCsv>(std::move(input_op), load_csv->file_, load_csv->with_header_,
-                                                load_csv->ignore_bad_, load_csv->delimiter_, load_csv->quote_, row_sym);
-
+            input_op = std::make_unique<plan::LoadCsv>(std::move(input_op), load_csv->file_, load_csv->with_header_,
+                                                       load_csv->ignore_bad_, load_csv->delimiter_, load_csv->quote_,
+                                                       load_csv->nullif_, row_sym);
           } else if (auto *foreach = utils::Downcast<query::Foreach>(clause)) {
             context.is_write_query = true;
             input_op = HandleForeachClause(foreach, std::move(input_op), *context.symbol_table, context.bound_symbols,

tests/e2e/load_csv/CMakeLists.txt

@@ -8,3 +8,6 @@ endfunction()
 
 copy_load_csv_e2e_python_files(load_csv.py)
 copy_load_csv_e2e_files(simple.csv)
+
+copy_load_csv_e2e_python_files(load_csv_nullif.py)
+copy_load_csv_e2e_files(nullif.csv)

tests/e2e/load_csv/load_csv_nullif.py

@@ -0,0 +1,53 @@
+# Copyright 2022 Memgraph Ltd.
+#
+# Use of this software is governed by the Business Source License
+# included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+# License, and you may not use this file except in compliance with the Business Source License.
+#
+# As of the Change Date specified in that file, in accordance with
+# the Business Source License, use of this software will be governed
+# by the Apache License, Version 2.0, included in the file
+# licenses/APL.txt.
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+from gqlalchemy import Memgraph
+
+NULLIF_CSV_FILE = "nullif.csv"
+
+
+def get_file_path(file: str) -> str:
+    parent_path = Path(__file__).parent.absolute()
+    return os.path.join(parent_path, file)
+
+
+def test_given_csv_when_nullif_then_all_identical_rows_are_null():
+    memgraph = Memgraph("localhost", 7687)
+
+    results = list(
+        memgraph.execute_and_fetch(
+            f"""LOAD CSV FROM '{get_file_path(NULLIF_CSV_FILE)}'
+            WITH HEADER NULLIF 'N/A' AS row
+            CREATE (n:Person {{name: row.name, age: row.age,
+            percentage: row.percentage, works_in_IT: row.works_in_IT}})
+            RETURN n
+            """
+        )
+    )
+
+    expected_properties = [
+        {"age": "10", "percentage": "15.0", "works_in_IT": "false"},
+        {"name": "John", "percentage": "35.4", "works_in_IT": "false"},
+        {"name": "Milewa", "age": "34", "works_in_IT": "false"},
+        {"name": "Lucas", "age": "50", "percentage": "12.5"},
+    ]
+    properties = [result["n"]._properties for result in results]
+
+    assert expected_properties == properties
+
+
+if __name__ == "__main__":
+    sys.exit(pytest.main([__file__, "-rA"]))

tests/e2e/load_csv/nullif.csv

@@ -0,0 +1,5 @@
+name,age,percentage,works_in_IT
+N/A,10,15.0,false
+John,N/A,35.4,false
+Milewa,34,N/A,false
+Lucas,50,12.5,N/A

tests/e2e/load_csv/workloads.yaml

@@ -1,3 +1,10 @@
+nullif_cluster: &nullif_cluster
+  cluster:
+    main:
+      args: ["--bolt-port", "7687", "--log-level=TRACE"]
+      log_file: "load_csv_log_file.txt"
+      validation_queries: []
+
 load_csv_cluster: &load_csv_cluster
   cluster:
     main:
@@ -9,6 +16,10 @@ load_csv_cluster: &load_csv_cluster
       validation_queries: []
 
 workloads:
+  - name: "LOAD CSV nullif"
+    binary: "tests/e2e/pytest_runner.sh"
+    args: ["load_csv/load_csv_nullif.py"]
+    <<: *nullif_cluster
   - name: "MATCH + LOAD CSV"
     binary: "tests/e2e/pytest_runner.sh"
     args: ["load_csv/load_csv.py"]