MongoDB- Return Array of existing fields by compare collection with Array of object

Question

I'm new to Mongo and trying compare a array with a documents of collections and return list of matching records.

Let me explain:First Array

I have a collection (user) with following documents:

> db.user.find().pretty()
{
    "_id" : ObjectId("57358220bf3e7d076b6ccdb1"),
    "name" : "Sunny",
    "phone" : "9417702107",
    "email" : "ssdhiman07@gmail.com"
}
{
    "_id" : ObjectId("57358242bf3e7d076b6ccdb2"),
    "name" : "Pal",
    "phone" : "9015719419",
    "email" : "ss998@gmail.com"
}
{
    "_id" : ObjectId("57358262bf3e7d076b6ccdb3"),
    "name" : "viveky",
    "phone" : "8826565107",
    "email" : "sds998@gmail.com"
}

Second Array: i have a array of objects that is come from Http request below is structure of array.

{
 "contacts" : [
            {
                    "name" : "Sunny",
                    "phone" : "9417702107"
            },
            {
                    "name" : "Sukhpal",
                    "phone" : "9015719419"
            },
            {
                    "name" : "anurag",
                    "phone" : "9988776655"
            },
            {
                    "name" : "vivek",
                    "phone" : "8826565107"
            }
         ]
} 

Now I want to know which objects of Second Array are exists in First Array and which doesn't . Comparison should on basis of phone only . And in result i want same Array as Second Array but with one extra field that is "exists":"true" or "exists":"false" . Something like this.

{
   "contacts" : [
            {
                    "name" : "Sunny",
                    "phone" : "9417702107"
                    "exists" :"true"
            },
            {
                    "name" : "pal",
                    "phone" : "90177668899"
                    "exists" :"false"
            }
          ]
  }

So for this i had tried something here is code of node.js with mongoos.

exports.matchcontacts = function(req, res, next)
{
  var response = {};   
  var conArray = req.body.contacts;
  var contact_list = [];

for(var i=0; i<conArray.length;i++)
{  
  var name = conArray[i].name;
  var phone = conArray[i].phone;

  Users.findOne({"phone":conArray[i].phone},function(err,data)
  {
        if(err) 
        {
            response = {"error" : true,"message" : "Error fetching data"};
        } 
        else if(!data)
          {
               contact_list.push({name:name,phone:phone,exists:"false"});
          }
        else 
         {
             contact_list.push({name:name,phone:phone,exists:"true"});
         }

    });
  }
  response = {"error":false,"contacts":contact_list};
  res.json(response);
};

But always got null {} empty result, and if i tried to get response inside Callback function then it return only single last compared value. Problem is in first method is that callback function return result very late so result always empty . and in second method loop override result and it also inefficient to use callback inside loop it will call no of time. So whole story i had explained

Now Please can anybody help me with code or suggest right way to get desired result thanks

Answer 1

Haven´t used mongodb, but the idea I would use is to first iterate your contacts and make a mapping of the phones to the corresponding object and mark them as non existent:

var obj = {};

for(var i=0; i<conArray.length;i++){
    obj[conArray[i].phone] = conArray[i];
    conArray[i].exists = false;
}

Then search in some way for the users that have those phones in your db, something like

var results = Users.find(records that have phone in Object.keys(obj) array)

Finally, you iterate your existant records and mark the corresponding contact

for(var i=0;i<results.length;i++){
    obj[results[i].phone].exists = true;
}