Merge pull request #14395 from Automattic/vkarpov15/gh-14353

fix(document): make `$clone` avoid converting subdocs into POJOs

Author: vkarpov15

lib/document.js

@@ -4735,7 +4735,7 @@ Document.prototype.$clone = function() {
   const clonedDoc = new Model();
   clonedDoc.$isNew = this.$isNew;
   if (this._doc) {
-    clonedDoc._doc = clone(this._doc);
+    clonedDoc._doc = clone(this._doc, { retainDocuments: true });
   }
   if (this.$__) {
     const Cache = this.$__.constructor;

lib/helpers/clone.js

@@ -36,10 +36,23 @@ function clone(obj, options, isArrayChild) {
   }
 
   if (isMongooseObject(obj)) {
-    // Single nested subdocs should apply getters later in `applyGetters()`
-    // when calling `toObject()`. See gh-7442, gh-8295
-    if (options && options._skipSingleNestedGetters && obj.$isSingleNested) {
-      options = Object.assign({}, options, { getters: false });
+    if (options) {
+      // Single nested subdocs should apply getters later in `applyGetters()`
+      // when calling `toObject()`. See gh-7442, gh-8295
+      if (options._skipSingleNestedGetters && obj.$isSingleNested) {
+        options = Object.assign({}, options, { getters: false });
+      }
+      if (options.retainDocuments && obj.$__ != null) {
+        const clonedDoc = obj.$clone();
+        if (obj.__index != null) {
+          clonedDoc.__index = obj.__index;
+        }
+        if (obj.__parentArray != null) {
+          clonedDoc.__parentArray = obj.__parentArray;
+        }
+        clonedDoc.$__parent = obj.$__parent;
+        return clonedDoc;
+      }
     }
     const isSingleNested = obj.$isSingleNested;
 

test/document.test.js

@@ -12070,6 +12070,27 @@ describe('document', function() {
     assert.strictEqual(clonedDoc.$session(), session);
   });
 
+  it('$clone() with single nested and doc array (gh-14353) (gh-11849)', async function() {
+    const schema = new mongoose.Schema({
+      subdocArray: [{
+        name: String
+      }],
+      subdoc: new mongoose.Schema({ name: String })
+    });
+    const Test = db.model('Test', schema);
+
+    const item = await Test.create({ subdocArray: [{ name: 'test 1' }], subdoc: { name: 'test 2' } });
+
+    const doc = await Test.findById(item._id);
+    const clonedDoc = doc.$clone();
+
+    assert.ok(clonedDoc.subdocArray[0].$__);
+    assert.ok(clonedDoc.subdoc.$__);
+
+    assert.deepEqual(doc.subdocArray[0], clonedDoc.subdocArray[0]);
+    assert.deepEqual(doc.subdoc, clonedDoc.subdoc);
+  });
+
   it('can create document with document array and top-level key named `schema` (gh-12480)', async function() {
     const AuthorSchema = new Schema({
       fullName: { type: 'String', required: true }