fix(document): make calling validate() with single nested subpath o…

…nly validate that single nested subpath

Fix #8626

lib/document.js

@@ -2392,18 +2392,31 @@ Document.prototype.$__validate = function(pathsToValidate, options, callback) {
 
 function _handlePathsToValidate(paths, pathsToValidate) {
   const _pathsToValidate = new Set(pathsToValidate);
+  const parentPaths = new Map([]);
   for (const path of pathsToValidate) {
     if (path.indexOf('.') === -1) {
       continue;
     }
     const pieces = path.split('.');
     let cur = pieces[0];
     for (let i = 1; i < pieces.length; ++i) {
-      _pathsToValidate.add(cur);
+      // Since we skip subpaths under single nested subdocs to
+      // avoid double validation, we need to add back the
+      // single nested subpath if the user asked for it (gh-8626)
+      parentPaths.set(cur, path);
       cur = cur + '.' + pieces[i];
     }
   }
-  return paths.filter(p => _pathsToValidate.has(p));
+
+  const ret = [];
+  for (const path of paths) {
+    if (_pathsToValidate.has(path)) {
+      ret.push(path);
+    } else if (parentPaths.has(path)) {
+      ret.push(parentPaths.get(path));
+    }
+  }
+  return ret;
 }
 
 /**

test/document.test.js

@@ -8827,14 +8827,16 @@ describe('document', function() {
 
   it('handles validating single nested paths when specified in `pathsToValidate` (gh-8626)', function() {
     const nestedSchema = Schema({
-      name: { type: String, validate: v => v.length > 2 }
+      name: { type: String, validate: v => v.length > 2 },
+      age: { type: Number, validate: v => v < 200 }
     });
     const schema = Schema({ nested: nestedSchema });
     const Model = mongoose.model('Test', schema);
 
-    const doc = new Model({ nested: { name: 'a' } });
+    const doc = new Model({ nested: { name: 'a', age: 9001 } });
     return doc.validate(['nested.name']).then(() => assert.ok(false), err => {
       assert.ok(err.errors['nested.name']);
+      assert.ok(!err.errors['nested.age']);
     });
   });
 });