Update RxDocument patch and incrementalPatch methods to merge the patch into the document using @fastify/deepmerge package.

This prevents an issue that can arise when calling `patch` or `incrementalPatch` with a patch value containing fields deeper that the top level of the document where values will be spliced out if the patch value does not contain a full copy of all fields instead of just the fields being patched.

Author: alex-zywicki

package.json

@@ -486,6 +486,7 @@
   },
   "dependencies": {
     "@babel/runtime": "7.28.4",
+    "@fastify/deepmerge": "3.1.0",
     "@types/clone": "2.1.4",
     "@types/cors": "2.8.19",
     "@types/express": "5.0.3",
@@ -634,4 +635,4 @@
     "webpack-dev-server": "5.2.2"
   },
   "packageManager": "[email protected]+sha512.a6b2f7906b721bba3d67d4aff083df04dad64c399707841b7acf00f6b133b7ac24255f2652fa22ae3534329dc6180534e98d17432037ff6fd140556e2bb3137e"
-}
+}

src/rx-document.ts

@@ -41,6 +41,18 @@ import { getSchemaByObjectPath } from './rx-schema-helper.ts';
 import { getWrittenDocumentsFromBulkWriteResponse, throwIfIsStorageWriteError } from './rx-storage-helper.ts';
 import { modifierFromPublicToInternal } from './incremental-write.ts';
 
+import deepmergeLib from '@fastify/deepmerge';
+
+// Create merge function with custom array behavior
+const merge = deepmergeLib({
+    mergeArray: (options) => {
+        return (target, source) => {
+            // Replace array entirely with source
+            return options.clone(source);
+        };
+    }
+});
+
 export const basePrototype = {
     get primaryPath() {
         const _this: RxDocument = this as any;
@@ -301,12 +313,7 @@ export const basePrototype = {
         patch: Partial<RxDocType>
     ) {
         const oldData = this._data;
-        const newData = clone(oldData);
-        Object
-            .entries(patch)
-            .forEach(([k, v]) => {
-                (newData as any)[k] = v;
-            });
+        const newData = merge(clone(oldData), patch);
         return this._saveData(newData, oldData);
     },
 
@@ -318,12 +325,7 @@ export const basePrototype = {
         patch: Partial<RxDocumentType>
     ): Promise<RxDocument<RxDocumentType>> {
         return this.incrementalModify((docData) => {
-            Object
-                .entries(patch)
-                .forEach(([k, v]) => {
-                    (docData as any)[k] = v;
-                });
-            return docData;
+            return merge(docData, patch) as typeof docData;
         });
     },