将mongo (使用mongoose)中的ref字段填充到不同的路径

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);

User.findOne({ name: 'John' })
  .populate('posts')
  .exec((err, user) => {
    if (err) {
      console.error(err);
      return;
    }
    console.log(user);
  });

User.findOne({ name: 'John' })
  .populate({
    path: 'posts',
    populate: { path: 'comments' }
  })
  .exec((err, user) => {
    if (err) {
      console.error(err);
      return;
    }
    console.log(user);
  });