how call synchronous mongo query in node js - mongodb

Question

I have to mongodb collection.
first i will call to coll1 and get ids.Then I want to call coll2 and search by ids and some other fields.
when I am calling to funtion it is returing undefined.
how I can wait untill i m not get result from funtion.
coll1 docs sample:
{
"_id" : ObjectId(""),
"container_id" : "56867887fdb391ff09d15e9",
"item_state" : [
{
"user_id" : 1,
"username" : "x",
"state" : "1"
},
{
"user_id" : 2,
"username" : "y",
"state" : "3"
}
],
"name" : "members test"
}
enter code here
function listMyWorkitems(user_id,callback) {
var user_id=1;
var workItemList = new Array();
db.collection('containers').find({'start_date':{"$lt":new Date(2017,02,11)}}).toArray(function(err,docs){
console.log("doc length");
console.log(docs.length);
for (var i = 0; i < docs.length; i++) {
db.collection('work_items').find({"$and":[{'container_id':docs[i]._id.toString()},{'item_state':{"$elemMatch":{'user_id':user_id,'is_active':1,'state':{"$in":["1","2","3"]}}}}]}).toArray(function(err,workDocs){
//console.log(workDocs);
for (var i = 0; i < workDocs.length; i++) {
for (var j = 0; j < workDocs[i].item_state.length; j++) {
var doc=workDocs[i].item_state[j]
workItemList.push(workDocs[i].name)
}
}
});
}
callback(workItemList);
});
}
listMyWorkitems(user_id,funtion(err,workItemList) {
console.log(workItemList)
});
I understand async auto concept but still it is returning empty list
here is code what i tried till now.. i done for collection 1 but once it is solve then i can query to collection 2 also..
var async = require('async');
var mongojs = require("mongojs");
var db = mongojs("localhost/mc_dev");
async.auto({
coll1task: function(callback) {
var idlist =[];
console.log("ids fetch from collection 1");
db.collection('containers').find({'start_date':{"$lt":new Date(2017,02,11)}}).toArray(function(err,docs){
docs.forEach(function(doc){
console.log(doc._id);
idlist.push(doc._id);
});});
callback(null,idlist);
},
finalcontrol: [
'coll1task',
function(results,callback) {
console.log(results.coll1task);
}
],
},
function(error, results) {
console.log('error = ', error)
console.log('results = ', results)
})

Answer 1

The best approach to do things asynchronously in node.js is by using modules like ASYNC or PROMISE.
You can visit async and get access to all the modules provided by this library.
Main modules provided by async library are
async.series=> this is what you can use in your case.
2.async.parallel
async.auto => I will suggest you to use this as it provide you to perform operations asynchronously as well as synchronously
Further more you can also use PROMISES as now they are the part of ECMA SCRIPT 6 there are various modules also which you can use to get this done.