Fix a bug to unflatten the doc with list of map with multiple entries correctly. (#1204)

Signed-off-by: Bo Zhang <bzhangam@amazon.com>
(cherry picked from commit da5eebb)

Author: bzhangam

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Features
 ### Enhancements
 ### Bug Fixes
+- Fix a bug to unflatten the doc with list of map with multiple entries correctly ([#1204](https://github.com/opensearch-project/neural-search/pull/1204)).
 ### Infrastructure
 ### Documentation
 ### Maintenance

src/main/java/org/opensearch/neuralsearch/util/ProcessorDocumentUtils.java

@@ -263,7 +263,7 @@ private static List<Object> handleList(List<Object> list) {
                 ProcessJsonObjectItem processJsonObjectItem = (ProcessJsonObjectItem) value;
                 Map<String, Object> tempMap = new HashMap<>();
                 unflattenSingleItem(processJsonObjectItem.key, processJsonObjectItem.value, tempMap);
-                targetList.set(targetList.size() - 1, tempMap);
+                processJsonObjectItem.targetMap.putAll(tempMap);
             } else {
                 targetList.add(value);
             }

src/test/java/org/opensearch/neuralsearch/util/ProcessorDocumentUtilsTests.java

@@ -134,6 +134,25 @@ public void testUnflatten_withList_thenSuccess() {
         assertEquals(expected, result);
     }
 
+    public void testUnflatten_withListOfObject_thenSuccess() {
+        Map<String, Object> map1 = Map.of("b.c", "d", "f", "h");
+        Map<String, Object> map2 = Map.of("b.c", "e", "f", "i");
+        List<Map<String, Object>> list = Arrays.asList(map1, map2);
+        Map<String, Object> input = Map.of("a", list);
+
+        Map<String, Object> nestedB1 = Map.of("c", "d");
+        Map<String, Object> expectedMap1 = Map.of("b", nestedB1, "f", "h");
+        Map<String, Object> nestedB2 = Map.of("c", "e");
+        Map<String, Object> expectedMap2 = Map.of("b", nestedB2, "f", "i");
+
+        List<Map<String, Object>> expectedList = Arrays.asList(expectedMap1, expectedMap2);
+
+        Map<String, Object> expected = Map.of("a", expectedList);
+
+        Map<String, Object> result = ProcessorDocumentUtils.unflattenJson(input);
+        assertEquals(expected, result);
+    }
+
     public void testUnflatten_withMixedContent_thenSuccess() {
         Map<String, Object> input = Map.of("a.b", "c", "d", "e", "f.g.h", "i");