Mongoose多对多关系

const mongoose = require('mongoose');

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

const groupSchema = new mongoose.Schema({
  name: String,
  members: [{ type: mongoose.Schema.Types.ObjectId, ref: 'User' }]
});

const User = mongoose.model('User', userSchema);
const Group = mongoose.model('Group', groupSchema);

const user1 = new User({ name: 'User 1' });
const user2 = new User({ name: 'User 2' });
const group1 = new Group({ name: 'Group 1' });
const group2 = new Group({ name: 'Group 2' });

user1.groups.push(group1);
user1.groups.push(group2);
user2.groups.push(group1);

user1.save();
user2.save();
group1.save();
group2.save();

User.findOne({ name: 'User 1' })
  .populate('groups')
  .exec((err, user) => {
    if (err) {
      console.error(err);
    } else {
      console.log(user.groups);
    }
  });