Fix issues with object type

Signed-off-by: John Mazanec <jmazane@amazon.com>

src/main/java/org/opensearch/knn/index/codec/derivedsource/NestedPerFieldDerivedVectorInjector.java

@@ -38,17 +38,12 @@ public class NestedPerFieldDerivedVectorInjector implements PerFieldDerivedVecto
     @Override
     public void inject(int parentDocId, Map<String, Object> sourceAsMap) throws IOException {
         // If the parent has the field, then it is just an object field.
-        if (getLowestDocIdForField(childFieldInfo.name, parentDocId) == parentDocId) {
+        int lowestDocIdForFieldWithParentAsOffset = getLowestDocIdForField(childFieldInfo.name, parentDocId);
+        if (lowestDocIdForFieldWithParentAsOffset == parentDocId) {
             injectObject(parentDocId, sourceAsMap);
             return;
         }
 
-        if (ParentChildHelper.splitPath(childFieldInfo.name).length > 2) {
-            // We do not support nested fields beyond one level
-            log.warn("Nested fields beyond one level are not supported. Field: {}", childFieldInfo.name);
-            return;
-        }
-
         // Setup the iterator. Return if no parent
         String childFieldName = ParentChildHelper.getChildField(childFieldInfo.name);
         String parentFieldName = ParentChildHelper.getParentField(childFieldInfo.name);
@@ -62,6 +57,10 @@ public void inject(int parentDocId, Map<String, Object> sourceAsMap) throws IOEx
             parentDocId
         );
 
+        if (nestedPerFieldParentToDocIdIterator.numChildren() == 0) {
+            return;
+        }
+
         // Initializes the parent field so that there is a list to put each of the children
         Object originalParentValue = sourceAsMap.get(parentFieldName);
         List<Map<String, Object>> reconstructedSource;

src/main/java/org/opensearch/knn/index/codec/derivedsource/NestedPerFieldParentToDocIdIterator.java

@@ -91,6 +91,14 @@ public int childId() {
         return children.get(currentChild);
     }
 
+    /**
+     *
+     * @return the number of children for this parent
+     */
+    public int numChildren() {
+        return children.size();
+    }
+
     /**
      * For parentDocId of this class, find the one just before it to be used for matching children.
      *
@@ -122,6 +130,10 @@ private int previousParent() throws IOException {
      * @throws IOException if there is an error reading the children
      */
     private List<Integer> getChildren() throws IOException {
+        if (this.parentDocId - this.previousParentDocId <= 1) {
+            return Collections.emptyList();
+        }
+
         // First, we need to get the currect PostingsEnum for the key as _nested_path and the value the actual parent
         // path.
         String childField = childFieldInfo.name;

src/test/java/org/opensearch/knn/integ/DerivedSourceIT.java

@@ -9,7 +9,6 @@
 import lombok.Builder;
 import lombok.Data;
 import lombok.SneakyThrows;
-import org.junit.Ignore;
 import org.opensearch.common.CheckedConsumer;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.xcontent.XContentFactory;
@@ -30,7 +29,7 @@
  * Integration tests for derived source feature for vector fields. Currently, with derived source, there are
  * a few gaps in functionality. Ignoring tests for now as feature is experimental.
  */
-@Ignore
+// @Ignore
 public class DerivedSourceIT extends KNNRestTestCase {
 
     private final static String NESTED_NAME = "test_nested";