How to make subsequent mongo call after successful call

Question

I have nodejs-mongo setup with db configured as follows (only one entry shown here)

{
 "filename":"type1.json","secs":72.4060092977,"platform":"mac","version":"1.3.0", "inputfile":"temp.mov"
},

Here are the mongo commands I am trying to replicate

db.perfR.distinct("platform") * (output: ["mac", "win"] ) *

db.perfR.distinct("version",{"platform":"win"}) * (output: ["1.3.0", "1.3.2"] ) *

db.perfR.find({"version":1.3.2,"platform":"win"},{"filename":1,"secs":1,"_id":0}) * (output: ["filename":"type1.json","secs":72.4060092977] ) *

So what I am trying to do is

for every platform 
for every version
    get filename
    get secs

Here is the code I have written thus far

function createPlatformDataSets(callback){                
var dbHost = "mongodb://mongo:27017/perfSample";
var mongodb = require('mongodb')

var platformDataSets = []
var platformq = "platform"
//get Instance of Mongoclient
var MongoClient = mongodb.MongoClient;

//Connecting to the Mongodb instance.
//Make sure your mongodb daemon mongod is running on port 27017 on localhost
MongoClient.connect(dbHost, function(err, db){
    if ( err ) throw err;
    //use the distinct() to retrive distinct platforms
    db.collection("perfR").distinct(platformq,function(err, platResultSet){
        if ( err ) throw err;
        var maxPlatCnt = platResultSet.length // 1
        if (maxPlatCnt == 0){
            console.log("Bad PlatfQ Query")
            callback(true)
        }
        var versionedPlatDataSet = 0
        for (p=0; p < platResultSet.length; p++){
            (function(index){
                var platform = platResultSet[index]
                var options = createOptions(platform);
                //Get Versions
                var versionq = "\"version\",{\"platform\":" + platform + "}"
                console.log("Versionq::"+versionq)
                var dataSets = [];
                //var versions = ["1.3.0", "1.3.2"]; // (select disctinct(version) from cpu where platform = plat)
                // Use distinct() to find distinct Versions
                db.collection("perfR").distinct(versionq,function(err, verResultSet){
                    if ( err ) throw err;
                    var maxVerCnt = verResultSet.length // 2
                    if (maxVerCnt == 0){
                        db.close()
                        console.log("Bad Versionq Query")
                        callback(true)
                        }
                    var dataSetResponseCnt = 0 
                    for ( v=0; v < verResultSet.length; v++){
                            (function(idx){
                                var dataq = "{platform:" + platform + ",version:" + version + "},{filename:1,secs:1,_id:0}"
                                // Use find() to find filename and secs for given version and platform 

                       db.collection("perfR").find(dataq,function(err, dataResultSet){
                                    if ( err ) throw err;
                                    if (dataResultSet.length == 0){
                                        console.log("Bad dataq Query")
                                        callback(true)
                                    }
                                    //do something with filename and secs
                                    dataSetResponseCnt++
                                    if (maxVerCnt == dataSetResponseCnt){
                                        var platformData = {"options":options, "labels":labels, "datasets":dataSets, "platform":platform}
                                        platformDataSets.push(platformData)
                                        if (versionedPlatDataSet == maxPlatCnt){
                                            db.close()
                                            callback(null,platformDataSets)
                                        }
                                    }
                                })
                            })(v)
                    }
                    versionedPlatDataSet++
            })(p)
        }
    }
}

At "1" I am able to retrive distinct platforms

But at "2" I get verResultSet.length to be zero.

Can someone point to me what is wrong?

(PS: This is my first serious async problem with javascript so bear with my code. All suggestions are welcome :) )

Answer 1

you can use Promises. so for example your code is going to be something like this:

return loadPlatforms().then(function (res){
    res.map(function(platform){
        loadVersion(platform).then(...)
    }
})

Answer 2

Your use of .distinct() isn't correct. You are passing a JSON-like string when the API actually takes two separate arguments (not including the callback). So the real code should in fact just be more or less what you originally showed:

var query = { platform: 'win' };
db.collection('perfR').distinct('version', query, function(err, verResultSet) {
  // ...
});