Mongodb findOne - return value [duplicate]

Question

I need to fetch id of user from collection 'users' by calling a function and return it's value.

fetchId = (name) => {
        User.findOne({name: name}, (err, user) => {
            return user._id;
        });
    };

But this implementation returns null. What is the way to fix it?

Answer 1

following your example, if you don't want to use promises, you can simply pass a callback from the caller and invoke the callback when you have the result since the call to mongo is asynchronous.

fetchId = (name, clb) => {
  User.findOne({name: name}, (err, user) => {
    clb(user._id);
  });
};

fetchId("John", id => console.log(id));

Otherwise you can use the promise based mechanism omitting the first callback and return the promise to the caller.

fetchId = name => {
  return User.findOne({name: name}).then(user => user.id);
}; 


fetchId("John")
 .then(id => console.log(id));