如何在mongoose中填充对象属性

const userSchema = new mongoose.Schema({
  name: String,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
});

const postSchema = new mongoose.Schema({
  title: String,
  content: String
});

const User = mongoose.model('User', userSchema);
const Post = mongoose.model('Post', postSchema);

const user = new User({ name: 'John' });
const post = new Post({ title: 'Hello', content: 'World' });

user.posts.push(post);
user.save();

User.findOne({ name: 'John' })
  .populate('posts')
  .exec((err, user) => {
    console.log(user.posts[0].title); // 输出：Hello
    console.log(user.posts[0].content); // 输出：World
  });