Enabled Filtering on Nested Vector fields with top level filters

Signed-off-by: Navneet Verma <navneev@amazon.com>

CHANGELOG.md

@@ -12,12 +12,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Maintenance
 ### Refactoring
 
-## [Unreleased 2.x](https://github.com/opensearch-project/k-NN/compare/2.11...2.x)
+## [Unreleased 2.x](https://github.com/opensearch-project/k-NN/compare/2.12...2.x)
 ### Features
 * Add parent join support for lucene knn [#1182](https://github.com/opensearch-project/k-NN/pull/1182)
 ### Enhancements
 * Increase Lucene max dimension limit to 16,000 [#1346](https://github.com/opensearch-project/k-NN/pull/1346)
 * Tuned default values for ef_search and ef_construction for better indexing and search performance for vector search [#1353](https://github.com/opensearch-project/k-NN/pull/1353)
+* Enabled Filtering on Nested Vector fields with top level filters [#1372](https://github.com/opensearch-project/k-NN/pull/1372)
 ### Bug Fixes
 * Fix use-after-free case on nmslib search path [#1305](https://github.com/opensearch-project/k-NN/pull/1305)
 * Allow nested knn field mapping when train model [#1318](https://github.com/opensearch-project/k-NN/pull/1318)

src/main/java/org/opensearch/knn/index/query/KNNQueryFactory.java

@@ -17,8 +17,10 @@
 import org.apache.lucene.search.join.BitSetProducer;
 import org.apache.lucene.search.join.DiversifyingChildrenByteKnnVectorQuery;
 import org.apache.lucene.search.join.DiversifyingChildrenFloatKnnVectorQuery;
+import org.apache.lucene.search.join.ToChildBlockJoinQuery;
 import org.opensearch.index.query.QueryBuilder;
 import org.opensearch.index.query.QueryShardContext;
+import org.opensearch.index.search.NestedHelper;
 import org.opensearch.knn.index.VectorDataType;
 import org.opensearch.knn.index.util.KNNEngine;
 
@@ -155,11 +157,27 @@ private static Query getFilterQuery(CreateQueryRequest createQueryRequest) {
                     createQueryRequest.k
                 )
             );
+            final Query filterQuery;
             try {
-                return createQueryRequest.getFilter().get().toQuery(queryShardContext);
+                filterQuery = createQueryRequest.getFilter().get().toQuery(queryShardContext);
             } catch (IOException e) {
                 throw new RuntimeException("Cannot create knn query with filter", e);
             }
+            // If k-NN Field is nested field then parentFilter will not be null. This parentFilter is set by the
+            // Opensearch core. Ref PR: https://github.com/opensearch-project/OpenSearch/pull/10246
+            if (queryShardContext.getParentFilter() != null) {
+                // if the filter is also a nested query clause then we should just return the same query without
+                // considering it to join with the parent documents.
+                if (new NestedHelper(queryShardContext.getMapperService()).mightMatchNestedDocs(filterQuery)) {
+                    return filterQuery;
+                }
+                // This condition will be hit when filters are getting applied on the top level fields and k-nn
+                // query field is a nested field. In this case we need to wrap the filter query with
+                // ToChildBlockJoinQuery to ensure parent documents which will be retrieved from filters can be
+                // joined with the child documents containing vector field.
+                return new ToChildBlockJoinQuery(filterQuery, queryShardContext.getParentFilter());
+            }
+            return filterQuery;
         }
         return null;
     }