Mongoose多对多关系

const mongoose = require('mongoose');

// 定义 User 模型
const userSchema = new mongoose.Schema({
  name: String,
});

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

// 定义 Group 模型
const groupSchema = new mongoose.Schema({
  name: String,
});

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

// 定义中间模型来表示多对多关系
const userGroupSchema = new mongoose.Schema({
  userId: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
  groupId: { type: mongoose.Schema.Types.ObjectId, ref: 'Group' },
});

const UserGroup = mongoose.model('UserGroup', userGroupSchema);

// 添加关系
async function addUserToGroup(userId, groupId) {
  const userGroup = new UserGroup({ userId, groupId });
  await userGroup.save();
}

// 查询属于某个组的所有用户
async function getUsersInGroup(groupId) {
  const userGroups = await UserGroup.find({ groupId }).populate('userId');
  return userGroups.map(ug => ug.userId);
}

// 使用示例
(async () => {
  await mongoose.connect('mongodb://localhost:27017/test', { useNewUrlParser: true, useUnifiedTopology: true });

  const user = new User({ name: 'Alice' });
  const group = new Group({ name: 'Developers' });

  await user.save();
  await group.save();

  await addUserToGroup(user._id, group._id);

  const usersInGroup = await getUsersInGroup(group._id);
  console.log(usersInGroup); // 输出属于该组的所有用户

  await mongoose.disconnect();
})();