Does mongoose findOne on model return a promise?

Question

I have a simple Node module that exports a function that makes a database query. The problem is that this function returns before the database query completes.

"use strict";

var mongoose = require('mongoose'),
    Model    = require('./entities/user/model'),
    _        = require('underscore');

let dao = new Model(mongoose);

module.exports.isAdmin = function(user_id) {
  var params = {'roles': 'admin'};

  dao.findOne(params, function(err, user) {
    if (err) {
      logger.error(err);
      return false;
    }
    if (_.indexOf(user.roles, 'admin') != -1) {
      logger.info("admin user: " + user._id);
      if (user._id == user_id) return true;
    }
    return false;
  });
};

isAdmin function searches the users collection in order to find out if user_id belongs to admin user.

The problem is that isAdmin function doesn't wait for the response of findOne query.

How could I force the isAdmin function to return only when query returns results ?

Answer 1

Because findOne is async function, one way to return from it is through callback function

module.exports.isAdmin = function(user_id, callback) {
  var params = {'roles': 'admin'};

  dao.findOne(params, function(err, user) {
    if (err) {
      logger.error(err);
      callback && callback(false);
    }
    if (_.indexOf(user.roles, 'admin') != -1) {
      logger.info("admin user: " + user._id);
      if (user._id == user_id)
          callback && callback(true);
    }
    callback && callback(true);
  });
};

isAdmin(userId, function(v) {
    console.log(v);
})

Another way is to get Promise in findOne, as this doc said, .exec() gives you a fully-fledged promise. Even with Promise, to meet you requirement, the result could be returned through callback function.

module.exports.isAdmin = function(user_id, callback) {
  var params = {'roles': 'admin'};

  var queryPromise = dao.findOne(params).exec();
  queryPromise.then(function(user) {
      if (_.indexOf(user.roles, 'admin') != -1) {
        logger.info("admin user: " + user._id);
        if (user._id == user_id)
          callback && callback(true);
      }
    }, function(err) {
      callback && callback(false);
  });
};