Fix FilterOperator to cache next element and avoid repeated consumption on hasNext() calls

core/src/main/java/org/opensearch/sql/planner/physical/FilterOperator.java

@@ -28,6 +28,7 @@ public class FilterOperator extends PhysicalPlan {
   @Getter private final PhysicalPlan input;
   @Getter private final Expression conditions;
   @ToString.Exclude private ExprValue next = null;
+  @ToString.Exclude private boolean nextPrepared = false;
 
   @Override
   public <R, C> R accept(PhysicalPlanNodeVisitor<R, C> visitor, C context) {
@@ -41,19 +42,34 @@ public List<PhysicalPlan> getChild() {
 
   @Override
   public boolean hasNext() {
+    if (!nextPrepared) {
+      prepareNext();
+    }
+    return next != null;
+  }
+
+  @Override
+  public ExprValue next() {
+    if (!nextPrepared) {
+      prepareNext();
+    }
+    ExprValue result = next;
+    next = null;
+    nextPrepared = false;
+    return result;
+  }
+
+  private void prepareNext() {
     while (input.hasNext()) {
       ExprValue inputValue = input.next();
       ExprValue exprValue = conditions.valueOf(inputValue.bindingTuples());
-      if (!(exprValue.isNull() || exprValue.isMissing()) && (exprValue.booleanValue())) {
+      if (!(exprValue.isNull() || exprValue.isMissing()) && exprValue.booleanValue()) {
         next = inputValue;
-        return true;
+        nextPrepared = true;
+        return;
       }
     }
-    return false;
-  }
-
-  @Override
-  public ExprValue next() {
-    return next;
+    next = null;
+    nextPrepared = true;
   }
 }

core/src/test/java/org/opensearch/sql/planner/physical/FilterOperatorTest.java

@@ -8,14 +8,24 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
+import static org.opensearch.sql.data.model.ExprValueUtils.LITERAL_FALSE;
 import static org.opensearch.sql.data.model.ExprValueUtils.LITERAL_MISSING;
 import static org.opensearch.sql.data.model.ExprValueUtils.LITERAL_NULL;
+import static org.opensearch.sql.data.model.ExprValueUtils.LITERAL_TRUE;
 import static org.opensearch.sql.data.type.ExprCoreType.INTEGER;
+import static org.opensearch.sql.planner.physical.PhysicalPlanDSL.filter;
 
 import com.google.common.collect.ImmutableMap;
 import java.util.LinkedHashMap;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayNameGeneration;
 import org.junit.jupiter.api.DisplayNameGenerator;
 import org.junit.jupiter.api.Test;
@@ -26,12 +36,22 @@
 import org.opensearch.sql.data.model.ExprValue;
 import org.opensearch.sql.data.model.ExprValueUtils;
 import org.opensearch.sql.expression.DSL;
+import org.opensearch.sql.expression.Expression;
 
 @ExtendWith(MockitoExtension.class)
 @DisplayNameGeneration(DisplayNameGenerator.ReplaceUnderscores.class)
 class FilterOperatorTest extends PhysicalPlanTestBase {
   @Mock private PhysicalPlan inputPlan;
 
+  @Mock private Expression condition;
+
+  private FilterOperator filterOperator;
+
+  @BeforeEach
+  public void setup() {
+    filterOperator = filter(inputPlan, condition);
+  }
+
   @Test
   public void filter_test() {
     FilterOperator plan =
@@ -82,4 +102,68 @@ public void missing_value_should_been_ignored() {
     List<ExprValue> result = execute(plan);
     assertEquals(0, result.size());
   }
+
+  @Test
+  public void testHasNextWhenInputHasNoElements() {
+    when(inputPlan.hasNext()).thenReturn(false);
+
+    assertFalse(
+        filterOperator.hasNext(), "hasNext() should return false when input has no elements");
+  }
+
+  @Test
+  public void testHasNextWithMatchingCondition() {
+    ExprValue inputValue = mock(ExprValue.class);
+    when(inputPlan.hasNext()).thenReturn(true).thenReturn(false);
+    when(inputPlan.next()).thenReturn(inputValue);
+    when(condition.valueOf(any())).thenReturn(LITERAL_TRUE);
+
+    assertTrue(filterOperator.hasNext(), "hasNext() should return true when condition matches");
+    assertEquals(
+        inputValue, filterOperator.next(), "next() should return the matching input value");
+  }
+
+  @Test
+  public void testHasNextWithNonMatchingCondition() {
+    ExprValue inputValue = mock(ExprValue.class);
+    when(inputPlan.hasNext()).thenReturn(true, false);
+    when(inputPlan.next()).thenReturn(inputValue);
+    when(condition.valueOf(any())).thenReturn(LITERAL_FALSE);
+
+    assertFalse(
+        filterOperator.hasNext(), "hasNext() should return false if no values match the condition");
+  }
+
+  @Test
+  public void testMultipleCallsToHasNextDoNotConsumeInput() {
+    ExprValue inputValue = mock(ExprValue.class);
+    when(inputPlan.hasNext()).thenReturn(true);
+    when(inputPlan.next()).thenReturn(inputValue);
+    when(condition.valueOf(any())).thenReturn(LITERAL_TRUE);
+
+    assertTrue(
+        filterOperator.hasNext(),
+        "First hasNext() call should return true if there is a matching value");
+    verify(inputPlan, times(1)).next();
+    assertTrue(
+        filterOperator.hasNext(),
+        "Subsequent hasNext() calls should still return true without advancing the input");
+    verify(inputPlan, times(1)).next();
+    assertEquals(
+        inputValue, filterOperator.next(), "next() should return the matching input value");
+    verify(inputPlan, times(1)).next();
+  }
+
+  @Test
+  public void testNextWithoutCallingHasNext() {
+    ExprValue inputValue = mock(ExprValue.class);
+    when(inputPlan.hasNext()).thenReturn(true, false);
+    when(inputPlan.next()).thenReturn(inputValue);
+    when(condition.valueOf(any())).thenReturn(LITERAL_TRUE);
+
+    assertEquals(
+        inputValue,
+        filterOperator.next(),
+        "next() should return the matching input value even if hasNext() was not called");
+  }
 }

integ-test/src/test/resources/correctness/bugfixes/3121.txt

@@ -0,0 +1 @@
+SELECT Origin, Dest FROM (SELECT * FROM opensearch_dashboards_sample_data_flights WHERE AvgTicketPrice > 100 GROUP BY Origin, Dest, AvgTicketPrice) AS flights WHERE AvgTicketPrice < 1000 ORDER BY AvgTicketPrice LIMIT 30