MEAN node js promise return undefinded - node.js

Question

I have a function that list all users and role refrenced to group. Now i have other function that take user role refid and returns group name. While trying to return name i got promise pending state.
function getAll() {
var deferred = Q.defer();
db.users.find().toArray(function(err, users) {
if (err) deferred.reject(err.name + ': ' + err.message);
// return users (without hashed passwords)
users = _.map(users, function(user) {
//console.log(user);
return _.omit(user, ['hash']);
});
users = _.map(users, function(user){
refId = {}= user['role'][0]['oid']['_id'];
//console.log(typeof refId);
user = _.omit(user, ['role']);
user.role = userRole.userRole(refId).then(function(err,rid){
if(err){
deferred.reject(err.name+':'+err.message);
}
deferred.resolve();
console.log(deferred.resolve(rid));
return deferred.promise;
console.log(deferred.promise);
});
return user;
//console.log(user);
})
// getRefId(users)
//console.log(users);
deferred.resolve(users);
});
function userRole(rid){
return new Promise((resolve, reject) => {
db.groups.findOne({"_id":rid}, function(err, doc){
if(err){
reject(err.name + ':' + err.message);
}
if(doc){
resolve({"name": doc.name});
//console.log(doc.name);
}
})
})
}

Answer 1

You you want to use Promises with Mongoose or the native Mongo driver for Node which you seem to be doing here, you don't have to use new Promise() everywhere. You can use the promises directly.
See the docs:
The official MongoDB Node.js driver provides both callback based as well as Promised based interaction with MongoDB allowing applications to take full advantage of the new features in ES6.
https://mongodb.github.io/node-mongodb-native/
Mongoose async operations, like .save() and queries, return Promises/A+ conformant promises. This means that you can do things like MyModel.findOne({}).then() and yield MyModel.findOne({}).exec() (if you're using co).
http://mongoosejs.com/docs/promises.html
Instead of this:
function userRole(rid){
return new Promise((resolve, reject) => {
db.groups.findOne({"_id":rid}, function(err, doc){
if(err){
reject(err.name + ':' + err.message);
}
if(doc){
resolve({"name": doc.name});
//console.log(doc.name);
}
})
})
}
you should be able to use:
function userRole(rid){
return db.groups.findOne({ _id: rid });
}
or:
const userRole = rid => db.groups.findOne({ _id: rid });
Now, in your version there is one problem - the promise will never get resolved if there is no error but the returned doc is falsy, which can happen. But there is no point in creating your own promises if the methods that you call return promises in the first place.
Even if you want custom error messages, you can still use:
function userRole(rid){
return db.groups.findOne({ _id: rid })
.catch(function (err) {
return Promise.reject(err.name + ':' + err.message);
});
}
or this with more modern syntax:
const userRole = rid => db.groups.findOne({ _id: rid })
.catch(err => Promise.reject(`${err.name}:${err.message}`));