fix(35): fix rollback incorrectly restoring nested objects when $set targets a dotted path

CHANGLOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 1.7.0 (2026-06-19)
+
+- Patch rollback incorrectly restoring nested objects - https://github.com/360Learning/mongo-bulk-data-migration/pull/36
+
 ## 1.6.0 (2026-02-25)
 
 - Automatic resume for empty queries using `FETCH_ALL` - https://github.com/360Learning/mongo-bulk-data-migration/pull/31

__tests__/MongoBulkDataMigration.rollback.test.ts

@@ -30,8 +30,8 @@
     collectionName: string;
     db: Db;
     id: string;
     query: any;
     projection: any;
     logger: LoggerInterface;
   };
   let loggerMock: LoggerInterface;
@@ -141,7 +141,7 @@
       const dataMigration = new MongoBulkDataMigration<DmDemoCollection>({
         ...DM_DEFAULT_SETUP,
         projection: { a: 1, b: 1 },
         update: ({ a, b }) => ({ $set: { a: a + b } }),
         options: {
           projectionBackupFilter: ['a'],
         },
@@ -206,7 +206,7 @@
       const insertedDocuments = await collection.find().toArray();
       const dataMigration = new MongoBulkDataMigration({
         ...DM_DEFAULT_SETUP,
         update: (doc: any) => ({ $set: { a: doc.a.b } }),
       });
 
       await dataMigration.update();
@@ -216,6 +216,25 @@
       expect(restoredDocuments).toEqual(insertedDocuments);
     });
 
+    it('should restore a nested object value when the target key already existed', async () => {
+      await collection.insertOne({
+        a: { source: { x: { nested: 1 } }, target: { x: { nested: 9 } } },
+      });
+      const insertedDocuments = await collection.find().toArray();
+      const dataMigration = new MongoBulkDataMigration({
+        ...DM_DEFAULT_SETUP,
+        projection: { a: 1 },
+        query: { 'a.source': { $exists: true } },
+        update: { $set: { 'a.target': { x: { nested: 1 } } } },
+      });
+
+      await dataMigration.update();
+      await dataMigration.rollback();
+
+      const restoredDocuments = await collection.find().toArray();
+      expect(restoredDocuments).toEqual(insertedDocuments);
+    });
+
     it('should restore removed documents', async () => {
       await collection.insertMany([{ key: 1 }, { key: 2 }, { key: 3 }]);
       const insertedDocuments = await collection.find().toArray();

__tests__/lib/computeRollbackQuery.unit.ts

@@ -54,6 +54,19 @@ describe('computeRollbackQuery', () => {
           $set: { 'nested.array': ['a', 'b'] },
         });
       });
+
+      it('should set back the nested original object value when the target already existed', async () => {
+        const updateQuery = {
+          $set: { 'a.b': { channels: { email: false, teams: true } } },
+        };
+        const backup = { a: { b: { channels: { email: true } } } };
+
+        const restoreQuery = computeRollbackQuery(updateQuery, backup);
+
+        expect(restoreQuery).toEqual({
+          $set: { 'a.b': { channels: { email: true } } },
+        });
+      });
     });
 
     describe('resulting from an $unset', () => {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@360-l/mongo-bulk-data-migration",
-  "version": "1.6.0",
+  "version": "1.7.0",
   "description": "MongoDB bulk data migration for node scripts",
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",

src/lib/computeRollbackQuery.ts

@@ -115,11 +115,10 @@ function computeRollbackSet(
         (setProperty) => key.startsWith(`${setProperty}.`),
       );
       if (setPropertyKeyStartsWith) {
-        const keyToSet = key.slice(setPropertyKeyStartsWith.length + 1);
-        rollbackSet[setPropertyKeyStartsWith] = {
-          ...(rollbackSet[setPropertyKeyStartsWith] ?? {}),
-          [keyToSet]: value,
-        };
+        rollbackSet[setPropertyKeyStartsWith] = _.get(
+          backup,
+          setPropertyKeyStartsWith,
+        );
         return rollbackSet;
       }