db = db.getSiblingDB('tavi');  // 选择 mydatabase
db.someCollection.insert({ initialized: true });  // 在 mydatabase 中插入一条数据
db.createUser(
  {
    user: "test",
    pwd: "test",
    roles: [
      {
        role: "readWrite",
        db: "tavi"
      }
    ]
  }
);