将Mongoose对象从id填充到新字段

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const UserSchema = new Schema({
  name: String,
  age: Number,
  // 引用另一个模型的id
  post: {
    type: Schema.Types.ObjectId,
    ref: 'Post'
  }
});

const PostSchema = new Schema({
  title: String,
  content: String
});

const User = mongoose.model('User', UserSchema);
const Post = mongoose.model('Post', PostSchema);

User.findById(userId)
  .populate('post') // 填充post字段
  .exec((err, user) => {
    if (err) {
      console.error(err);
      return;
    }
    console.log(user);
  });