fix(document): support setting nested path to itself when it has nest…

…ed subpaths

Fix #9313

lib/helpers/document/compile.js

@@ -141,7 +141,7 @@ function defineKey(prop, subprops, prototype, prefix, keys, options) {
         if (v != null && v.$__isNested) {
           // Convert top-level to POJO, but leave subdocs hydrated so `$set`
           // can handle them. See gh-9293.
-          v = v.$__parent.get(v.$__.nestedPath);
+          v = v.$__parent.get(path);
         }
         const doc = this.$__[scopeSymbol] || this;
         doc.$set(path, v);

test/document.test.js

@@ -9164,6 +9164,39 @@ describe('document', function() {
     });
   });
 
+  it('doesnt wipe out nested paths when setting a nested path to itself (gh-9313)', function() {
+    const schema = new Schema({
+      nested: {
+        prop1: { type: Number, default: 50 },
+        prop2: {
+          type: String,
+          enum: ['val1', 'val2'],
+          default: 'val1',
+          required: true
+        },
+        prop3: {
+          prop4: { type: Number, default: 0 }
+        }
+      }
+    });
+
+    const Model = db.model('Test', schema);
+
+    return co(function*() {
+      let doc = yield Model.create({});
+
+      doc = yield Model.findById(doc);
+
+      doc.nested = doc.nested;
+
+      assert.equal(doc.nested.prop2, 'val1');
+      yield doc.save();
+
+      const fromDb = yield Model.collection.findOne({ _id: doc._id });
+      assert.equal(fromDb.nested.prop2, 'val1');
+    });
+  });
+
   it('allows saving after setting document array to itself (gh-9266)', function() {
     const Model = db.model('Test', Schema({ keys: [{ _id: false, name: String }] }));