Cypher : support Unwind with nested list, fixes #3329

engine/src/main/java/com/arcadedb/query/opencypher/executor/CypherExecutionPlan.java

@@ -599,32 +599,35 @@ private AbstractExecutionStep buildExecutionStepsWithOrder(final CommandContext
     if (typeCountStep != null)
       return typeCountStep;
 
-    // Special case: RETURN without MATCH (standalone expressions)
-    // E.g., RETURN abs(-42), RETURN 1+1
-    if (statement.getMatchClauses().isEmpty() && statement.getReturnClause() != null &&
-        clausesInOrder.stream().noneMatch(c -> c.getType() == ClauseEntry.ClauseType.UNWIND)) {
-      // Create a dummy row to evaluate expressions against
-      final ResultInternal dummyRow = new ResultInternal();
-      final List<Result> singleRow = List.of(dummyRow);
-
-      // Return the single row via an initial step
-      currentStep = new AbstractExecutionStep(context) {
-        private boolean consumed = false;
-
-        @Override
-        public ResultSet syncPull(final CommandContext ctx, final int nRecords) {
-          if (consumed) {
-            return new IteratorResultSet(List.<ResultInternal>of().iterator());
+    // Special case: Standalone WITH, UNWIND, or RETURN
+    if (!clausesInOrder.isEmpty()) {
+      final ClauseEntry.ClauseType firstClauseType = clausesInOrder.get(0).getType();
+      if (firstClauseType == ClauseEntry.ClauseType.WITH ||
+          firstClauseType == ClauseEntry.ClauseType.UNWIND ||
+          (firstClauseType == ClauseEntry.ClauseType.RETURN && statement.getMatchClauses().isEmpty())) {
+        // Create a dummy row to evaluate expressions against
+        final ResultInternal dummyRow = new ResultInternal();
+        final List<Result> singleRow = List.of(dummyRow);
+
+        // Return the single row via an initial step
+        currentStep = new AbstractExecutionStep(context) {
+          private boolean consumed = false;
+
+          @Override
+          public ResultSet syncPull(final CommandContext ctx, final int nRecords) {
+            if (consumed) {
+              return new IteratorResultSet(List.<ResultInternal>of().iterator());
+            }
+            consumed = true;
+            return new IteratorResultSet(singleRow.iterator());
           }
-          consumed = true;
-          return new IteratorResultSet(singleRow.iterator());
-        }
 
-        @Override
-        public String prettyPrint(final int depth, final int indent) {
-          return "  ".repeat(Math.max(0, depth * indent)) + "+ DUMMY ROW (for standalone expressions)";
-        }
-      };
+          @Override
+          public String prettyPrint(final int depth, final int indent) {
+            return "  ".repeat(Math.max(0, depth * indent)) + "+ DUMMY ROW (for standalone expressions)";
+          }
+        };
+      }
     }
 
     // Process clauses in order

engine/src/main/java/com/arcadedb/query/opencypher/executor/steps/CreateStep.java

@@ -31,6 +31,7 @@
 import com.arcadedb.query.opencypher.ast.NodePattern;
 import com.arcadedb.query.opencypher.ast.PathPattern;
 import com.arcadedb.query.opencypher.ast.RelationshipPattern;
+import com.arcadedb.query.opencypher.ast.Direction;
 import com.arcadedb.query.opencypher.parser.CypherASTBuilder;
 import com.arcadedb.query.sql.executor.*;
 
@@ -205,8 +206,16 @@ private void createPath(final PathPattern pathPattern, final ResultInternal resu
       // Create relationships between vertices
       for (int i = 0; i < pathPattern.getRelationshipCount(); i++) {
         final RelationshipPattern relPattern = pathPattern.getRelationship(i);
-        final Vertex fromVertex = vertices.get(i);
-        final Vertex toVertex = vertices.get(i + 1);
+        final Vertex fromVertex;
+        final Vertex toVertex;
+
+        if (relPattern.getDirection() == Direction.IN) {
+          fromVertex = vertices.get(i + 1);
+          toVertex = vertices.get(i);
+        } else {
+          fromVertex = vertices.get(i);
+          toVertex = vertices.get(i + 1);
+        }
 
         final Edge edge = createEdge(fromVertex, toVertex, relPattern, result);
         if (relPattern.getVariable() != null) {

engine/src/main/java/com/arcadedb/query/opencypher/executor/steps/MergeStep.java

@@ -31,6 +31,7 @@
 import com.arcadedb.query.opencypher.ast.NodePattern;
 import com.arcadedb.query.opencypher.ast.PathPattern;
 import com.arcadedb.query.opencypher.ast.RelationshipPattern;
+import com.arcadedb.query.opencypher.ast.Direction;
 import com.arcadedb.query.opencypher.ast.SetClause;
 import com.arcadedb.query.opencypher.executor.CypherFunctionFactory;
 import com.arcadedb.query.opencypher.executor.ExpressionEvaluator;
@@ -278,8 +279,16 @@ private boolean mergePath(final PathPattern pathPattern, final ResultInternal re
     // Merge relationships between vertices
     for (int i = 0; i < pathPattern.getRelationshipCount(); i++) {
       final RelationshipPattern relPattern = pathPattern.getRelationship(i);
-      final Vertex fromVertex = vertices.get(i);
-      final Vertex toVertex = vertices.get(i + 1);
+      final Vertex fromVertex;
+      final Vertex toVertex;
+
+      if (relPattern.getDirection() == Direction.IN) {
+        fromVertex = vertices.get(i + 1);
+        toVertex = vertices.get(i);
+      } else {
+        fromVertex = vertices.get(i);
+        toVertex = vertices.get(i + 1);
+      }
 
       // Try to find existing relationship
       Edge edge = findEdge(fromVertex, toVertex, relPattern, result);

engine/src/test/java/com/arcadedb/query/opencypher/OpenCypherIssuesTest.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright © 2021-present Arcade Data Ltd (info@arcadedata.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * SPDX-FileCopyrightText: 2021-present Arcade Data Ltd (info@arcadedata.com)
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package com.arcadedb.query.opencypher;
+
+import com.arcadedb.database.Database;
+import com.arcadedb.database.DatabaseFactory;
+import com.arcadedb.query.sql.executor.Result;
+import com.arcadedb.query.sql.executor.ResultSet;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class OpenCypherIssuesTest {
+  private Database database;
+
+  @BeforeEach
+  void setUp() {
+    database = new DatabaseFactory("./target/databases/testopencypher-issues").create();
+  }
+
+  @AfterEach
+  void tearDown() {
+    if (database != null) {
+      database.drop();
+      database = null;
+    }
+  }
+
+  @Test
+  void unwindWithNestedList() {
+    final String query = "WITH [[1, 2], [3, 4], []] AS nested\n" +
+        "UNWIND nested AS x\n" +
+        "UNWIND x AS y\n" +
+        "RETURN count(y) AS total";
+    final ResultSet result = database.query("opencypher", query);
+    assertTrue(result.hasNext());
+    final Result row = result.next();
+    assertEquals(4L, (long) row.getProperty("total"));
+    assertFalse(result.hasNext());
+  }
+}