Strip filter_type from options and pass as typed FilterType to VectorSearchIndex

Signed-off-by: Eric Wei <mengwei.eric@gmail.com>

Author: mengweieric

opensearch/src/main/java/org/opensearch/sql/opensearch/storage/VectorSearchIndex.java

@@ -26,18 +26,32 @@ public class VectorSearchIndex extends OpenSearchIndex {
   private final String field;
   private final float[] vector;
   private final Map<String, String> options;
+  private final FilterType filterType; // null means default (POST)
 
   public VectorSearchIndex(
       OpenSearchClient client,
       Settings settings,
       String indexName,
       String field,
       float[] vector,
-      Map<String, String> options) {
+      Map<String, String> options,
+      FilterType filterType) {
     super(client, settings, indexName);
     this.field = field;
     this.vector = vector;
     this.options = options;
+    this.filterType = filterType;
+  }
+
+  /** Backward-compatible constructor — defaults to no explicit filter type. */
+  public VectorSearchIndex(
+      OpenSearchClient client,
+      Settings settings,
+      String indexName,
+      String field,
+      float[] vector,
+      Map<String, String> options) {
+    this(client, settings, indexName, field, vector, options, null);
   }
 
   @Override

opensearch/src/main/java/org/opensearch/sql/opensearch/storage/VectorSearchTableFunctionImplementation.java

@@ -100,7 +100,14 @@ public Table applyArguments() {
     Map<String, String> options = parseOptions(optionStr);
     validateOptions(options);
 
-    return new VectorSearchIndex(client, settings, tableName, fieldName, vector, options);
+    // Strip filter_type — it's a SQL-layer directive, not a knn parameter
+    FilterType filterType = null;
+    if (options.containsKey("filter_type")) {
+      filterType = FilterType.fromString(options.remove("filter_type"));
+    }
+
+    return new VectorSearchIndex(
+        client, settings, tableName, fieldName, vector, options, filterType);
   }
 
   private float[] parseVector(String vectorLiteral) {

opensearch/src/test/java/org/opensearch/sql/opensearch/storage/VectorSearchIndexTest.java

@@ -6,6 +6,7 @@
 package org.opensearch.sql.opensearch.storage;
 
 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 java.util.LinkedHashMap;
@@ -139,6 +140,21 @@ void buildKnnQueryJsonNonNumericOptionRenderedQuoted() {
     assertTrue(json.contains("\"k\":5"), "Numeric option should be unquoted");
   }
 
+  @Test
+  void buildKnnQueryJsonExcludesFilterType() {
+    LinkedHashMap<String, String> options = new LinkedHashMap<>();
+    options.put("k", "5");
+
+    VectorSearchIndex index =
+        new VectorSearchIndex(
+            client, settings, "test-index", "embedding",
+            new float[] {1.0f}, options, FilterType.EFFICIENT);
+
+    String json = index.buildKnnQueryJson();
+    assertFalse(json.contains("filter_type"), "filter_type should not appear in knn JSON");
+    assertTrue(json.contains("\"k\":5"), "k should still be present");
+  }
+
   @Test
   void isInstanceOfOpenSearchIndex() {
     VectorSearchIndex index =