dhruva_RP-13223-Parent_field_access_from_nested_query

src/main/java/com/yelp/nrtsearch/server/doc/SegmentDocLookup.java

@@ -17,6 +17,7 @@
 
 import com.yelp.nrtsearch.server.field.FieldDef;
 import com.yelp.nrtsearch.server.field.IndexableFieldDef;
+import com.yelp.nrtsearch.server.index.IndexState;
 import java.io.IOException;
 import java.util.Collection;
 import java.util.HashMap;
@@ -96,6 +97,9 @@ public boolean containsValue(Object value) {
    * Get the {@link LoadedDocValues} for a given field. Creates a new instance or uses one from the
    * cache. The data is loaded for the current set document id.
    *
+   * <p>If the field is not found in the current document and it is a nested document, it will
+   * attempt to find the field in the parent document using the NESTED_DOCUMENT_OFFSET field.
+   *
    * @param key field name
    * @return {@link LoadedDocValues} implementation for the given field
    * @throws IllegalArgumentException if the field does not support doc values, if there is a
@@ -128,9 +132,92 @@ public LoadedDocValues<?> get(Object key) {
       throw new IllegalArgumentException(
           "Could not set doc: " + docId + ", field: " + fieldName, e);
     }
+    if (docValues.isEmpty()) {
+      LoadedDocValues<?> parentDocValues = tryGetFromParentDocument(fieldName);
+      if (parentDocValues != null) {
+        return parentDocValues;
+      }
+    }
     return docValues;
   }
 
+  /**
+   * Attempt to retrieve the field from the parent document using NESTED_DOCUMENT_OFFSET.
+   *
+   * @param fieldName the name of the field to retrieve
+   * @return LoadedDocValues from parent document, or null if not found or not a nested document
+   * @throws IllegalArgumentException if there are issues accessing the offset field or parent
+   *     document
+   */
+  private LoadedDocValues<?> tryGetFromParentDocument(String fieldName) {
+    FieldDef offsetFieldDef;
+    try {
+      offsetFieldDef = IndexState.getMetaField(IndexState.NESTED_DOCUMENT_OFFSET);
+    } catch (IllegalArgumentException e) {
+      // This can happen if the meta field doesn't exist, which means the caller was not a nested
+      // document
+      return null;
+    }
+
+    if (!(offsetFieldDef instanceof IndexableFieldDef<?> offsetIndexableFieldDef)) {
+      throw new IllegalArgumentException("NESTED_DOCUMENT_OFFSET field cannot have doc values");
+    }
+
+    LoadedDocValues<?> offsetDocValues;
+    try {
+      offsetDocValues = offsetIndexableFieldDef.getDocValues(context);
+    } catch (IOException e) {
+      throw new IllegalArgumentException(
+          "Could not get doc values for NESTED_DOCUMENT_OFFSET field", e);
+    }
+
+    try {
+      offsetDocValues.setDocId(docId);
+    } catch (IOException e) {
+      throw new IllegalArgumentException(
+          "Could not set doc: " + docId + " for NESTED_DOCUMENT_OFFSET field", e);
+    }
+
+    if (offsetDocValues.isEmpty()) {
+      return null;
+    }
+
+    Object offsetValue = offsetDocValues.getFirst();
+    int offset = ((Number) offsetValue).intValue();
+
+    // The offset represents the exact number of documents to jump forward to reach the parent
+    int parentDocId = docId + offset;
+
+    FieldDef fieldDef = fieldDefLookup.apply(fieldName);
+    if (fieldDef == null) {
+      throw new IllegalArgumentException("Field does not exist: " + fieldName);
+    }
+    if (!(fieldDef instanceof IndexableFieldDef<?> indexableFieldDef)) {
+      throw new IllegalArgumentException("Field cannot have doc values: " + fieldName);
+    }
+
+    LoadedDocValues<?> parentDocValues;
+    try {
+      parentDocValues = indexableFieldDef.getDocValues(context);
+    } catch (IOException e) {
+      throw new IllegalArgumentException(
+          "Could not get doc values for parent field: " + fieldName, e);
+    }
+
+    try {
+      parentDocValues.setDocId(parentDocId);
+    } catch (IOException e) {
+      throw new IllegalArgumentException(
+          "Could not set parent doc: " + parentDocId + ", field: " + fieldName, e);
+    }
+
+    if (!parentDocValues.isEmpty()) {
+      return parentDocValues;
+    }
+
+    return null;
+  }
+
   @Override
   public LoadedDocValues<?> put(String key, LoadedDocValues<?> value) {
     throw new UnsupportedOperationException();

src/main/java/com/yelp/nrtsearch/server/field/ObjectFieldDef.java

@@ -31,7 +31,6 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 import org.apache.lucene.document.BinaryDocValuesField;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.StoredField;
@@ -74,27 +73,36 @@ public void parseFieldWithChildren(
       List<Map<String, Object>> fieldValueMaps = new ArrayList<>();
       fieldValues.stream().map(e -> gson.fromJson(e, Map.class)).forEach(fieldValueMaps::add);
 
-      List<Document> childDocuments =
-          fieldValueMaps.stream()
-              .map(e -> createChildDocument(e, facetHierarchyPaths))
-              .collect(Collectors.toList());
+      int totalDocs = fieldValueMaps.size();
+      List<Document> childDocuments = new ArrayList<>(totalDocs);
+
+      for (int i = 0; i < totalDocs; i++) {
+        // Calculate offset as n-i (total docs minus current index)
+        int offset = totalDocs - i;
+        childDocuments.add(createChildDocument(fieldValueMaps.get(i), facetHierarchyPaths, offset));
+      }
+
       documentsContext.addChildDocuments(this.getName(), childDocuments);
     }
   }
 
   /**
    * create a new lucene document for each nested object
    *
-   * @param fieldValue
-   * @param facetHierarchyPaths
+   * @param fieldValue the field value to include in the document
+   * @param facetHierarchyPaths facet hierarchy paths
+   * @param offset the offset value to set for this document (n-i)
    * @return lucene document
    */
   private Document createChildDocument(
-      Map<String, Object> fieldValue, List<List<String>> facetHierarchyPaths) {
+      Map<String, Object> fieldValue, List<List<String>> facetHierarchyPaths, int offset) {
     Document document = new Document();
     parseFieldWithChildrenObject(document, List.of(fieldValue), facetHierarchyPaths);
     ((IndexableFieldDef<?>) (IndexState.getMetaField(IndexState.NESTED_PATH)))
         .parseDocumentField(document, List.of(this.getName()), List.of());
+
+    ((IndexableFieldDef<?>) (IndexState.getMetaField(IndexState.NESTED_DOCUMENT_OFFSET)))
+        .parseDocumentField(document, List.of(String.valueOf(offset)), List.of());
     return document;
   }
 

src/main/java/com/yelp/nrtsearch/server/index/IndexState.java

@@ -83,6 +83,7 @@ public abstract class IndexState implements Closeable {
   public static final String NESTED_PATH = "_nested_path";
   public static final String ROOT = "_root";
   public static final String FIELD_NAMES = "_field_names";
+  public static final String NESTED_DOCUMENT_OFFSET = "_offset";
 
   private static final Logger logger = LoggerFactory.getLogger(IndexState.class);
   private final GlobalState globalState;
@@ -564,6 +565,17 @@ private static Map<String, FieldDef> getPredefinedMetaFields(GlobalState globalS
                     .setSearch(true)
                     .setMultiValued(true)
                     .build(),
+                FieldDefCreator.createContext(globalState)),
+        NESTED_DOCUMENT_OFFSET,
+        FieldDefCreator.getInstance()
+            .createFieldDef(
+                NESTED_DOCUMENT_OFFSET,
+                Field.newBuilder()
+                    .setName(NESTED_DOCUMENT_OFFSET)
+                    .setType(FieldType.INT)
+                    .setSearch(true)
+                    .setStoreDocValues(true)
+                    .build(),
                 FieldDefCreator.createContext(globalState)));
   }
 }