Q.js variables passing in parallel flows - node.js

Question

While implementing promises got this code:
var MongoClient = require('mongodb').MongoClient
MongoClient.connect(db_uri, function(err, db) {
if(err) throw err;
var ccoll = db.collection('cdata');
app.locals.dbstore = db;
}
var json= {}
//Auth is a wrapped mongo collection
var Auth = app.locals.Auth;
var coll = app.locals.dbstore.collection('data');
var ucoll = app.locals.dbstore.collection('udata');
var ccoll = app.locals.dbstore.collection('cdata');
var Q = require('q');
//testing with certain _id in database
var _id = require('mongodb').ObjectID('530ede30ae797394160a6856');
//Auth.getUserById = collection.findOne()
var getUser = Q.nbind(Auth.getUserById, Auth);
//getUserInfo gives a detailed information about each user
var getUserInfo = Q.nbind(ucoll.findOne, ucoll);
var getUserData = Q.nbind(ccoll.findOne, ccoll);
//"upr" is a group of users
//getUsers gives me a list of users, belonging to this group
var getUsers = Q.nbind(ucoll.find, ucoll);
//Auth.getUserById = collection.find()
var listUsers = Q.nbind(Auth.listUsers, Auth);
var uupr = {}
var cupr = {}
getUserInfo({_id:_id})
.then(function(entry){
console.log('entry:', entry);
uupr = entry;
var queue = [getUsers({upr:entry.name}), getUserData({_id:entry._id})]
return Q.all(queue);
}
)
.then(function(array2){
console.log('array2:', array2);
cupr = array2[1]
var cursor = array2[0]
var cfill = Q.nbind(cursor.toArray, cursor);
return cfill();
}
)
.then(function(data){
json = {data:data, uupr:uupr, cupr:cupr}
console.log('json:', json)
res.render('test', {json : JSON.stringify(json)})
}
)
Its work can be described by a diagram:
getUserInfo()==>(entry)--+-->getUsers()=====>array2[0]--+-->populate user list===>data--->render
| |
+-->getUserData()==>array2[1]--+
I've used external variables uupr and cupr to store data from first .then calls.
So I have two problems:
1) Avoid using external variables.
2) rearrange code to get alternative flow diagram.
getUserInfo()==>(entry)--+-->getUsers()==>usersList-->populate user list==>usersData-+->render
| |
+-->getUserData()====>uprData-------------------------------+
Any advice is appreciated

Answer 1

Try something along the lines of this pseudo-code:
getUserInfo().then(function(userInfo) {
return Q.all([
userInfo,
getUsers(... userInfo ...).then(convert to array),
getUserData(... userInfo ...)
])
}).spread(function(userInfo, usersArray, userData) {
res.render(...)
}, function(err) {
handle the error
}).done()

Answer 2

You can simply nest them:
getUserInfo({_id:_id})
.then(function(entry){
console.log('entry:', entry);
return Q.all([
getUsers({upr:entry.name}),
getUserData({_id:entry._id})
]);
.spread(function(cursor, cupr) {
console.log('array2:', [cursor, cupr]);
return Q.ninvoke(cursor, "toArray")
.then(function(data){
return {data:data, uupr:entry, cupr:cupr};
});
});
}).then(function(json) {
console.log('json:', json)
res.render('test', {json: JSON.stringify(json)})
});
Now, to let the toArray not wait for the getUserData result, just do those in parallel:
getUserInfo({_id:_id})
.then(function(entry){
console.log('entry:', entry);
return Q.all([
getUsers({upr:entry.name}).invoke("toArray"),
getUserData({_id:entry._id})
]);
.spread(function(data, cupr) {
return {data:data, uupr:entry, cupr:cupr};
});
}).then(function(json) {
console.log('json:', json)
res.render('test', {json: JSON.stringify(json)})
});
(Using invoke instead an explicit then)