fix(map): clean modified subpaths when overwriting values in map of subdocs

lib/types/map.js

@@ -9,6 +9,7 @@ const handleSpreadDoc = require('../helpers/document/handleSpreadDoc');
 const util = require('util');
 const specialProperties = require('../helpers/specialProperties');
 const isBsonType = require('../helpers/isBsonType');
+const cleanModifiedSubpaths = require('../helpers/document/cleanModifiedSubpaths');
 
 const populateModelSymbol = require('../helpers/symbols').populateModelSymbol;
 
@@ -157,7 +158,13 @@ class MongooseMap extends Map {
     super.set(key, value);
 
     if (parent != null && parent.$__ != null && !deepEqual(value, priorVal)) {
-      parent.markModified(fullPath.call(this));
+      const path = fullPath.call(this);
+      parent.markModified(path);
+      // If overwriting the full document array or subdoc, make sure to clean up any paths that were modified
+      // before re: #15108
+      if (this.$__schemaType.$isMongooseDocumentArray || this.$__schemaType.$isSingleNested) {
+        cleanModifiedSubpaths(parent, path);
+      }
     }
 
     // Delay calculating full path unless absolutely necessary, because string

test/types.map.test.js

@@ -1103,4 +1103,51 @@ describe('Map', function() {
     assert.equal(doc.addresses.get('home').length, 1);
     assert.equal(doc.addresses.get('home')[0].city, 'London');
   });
+
+  it('clears nested changes in subdocs (gh-15108)', async function() {
+    const CarSchema = new mongoose.Schema({
+      owners: {
+        type: Map,
+        of: {
+          name: String
+        }
+      }
+    });
+    const CarModel = db.model('Car', CarSchema);
+    const car = await CarModel.create({
+      owners: { abc: { name: 'John' } }
+    });
+
+    car.owners.get('abc').name = undefined;
+    car.owners.delete('abc');
+    assert.deepStrictEqual(car.getChanges(), { $unset: { 'owners.abc': 1 } });
+    await car.save();
+
+    const doc = await CarModel.findById(car._id);
+    assert.strictEqual(doc.owners.get('abc'), undefined);
+  });
+
+  it('clears nested changes in doc arrays (gh-15108)', async function() {
+    const CarSchema = new mongoose.Schema({
+      owners: {
+        type: Map,
+        of: [{
+          _id: false,
+          name: String
+        }]
+      }
+    });
+    const CarModel = db.model('Car', CarSchema);
+    const car = await CarModel.create({
+      owners: { abc: [{ name: 'John' }] }
+    });
+
+    car.owners.get('abc')[0].name = undefined;
+    car.owners.set('abc', [{ name: 'Bill' }]);
+    assert.deepStrictEqual(car.getChanges(), { $inc: { __v: 1 }, $set: { 'owners.abc': [{ name: 'Bill' }] } });
+    await car.save();
+
+    const doc = await CarModel.findById(car._id);
+    assert.deepStrictEqual(doc.owners.get('abc').toObject(), [{ name: 'Bill' }]);
+  });
 });