use string out of a mongodb function

Question

need some help with node js and mongodb how can I return the resp? cause now it returns "undefined";

function(table, where, to_select) {
  var r = {};
  MongoClient.connect("mongodb://127.0.0.1:27017/db", function(err, db) {
    if(!err) {
      collection = db.collection(table);
      collection.find(where, to_select).toArray(function(err, resp) {
        r.t = resp; // return THIS
      });
    }
  });
  return r.t; //returns undefined //
}

Mykola Borysyuk · Accepted Answer · 2016-08-28 08:01:59Z

1

You need to use callback because DB query in asynchronous operation. So your return gets called before find actually return results. Here is the fix

function runQuery(table,where,to_select, callback){ MongoClient.connect("mongodb://127.0.0.1:27017/db", function(err, db) { if (err) {return callback(err);} collection = db.collection(table); collection.find(where,to_select).toArray(function(err, resp) { callback(err, resp); }); }); }

And to call function you need

runQuery(table, where, select, function(err, results){
   ///do something with results.
});

Hope this helps.

edited Aug 28, 2016 at 8:01

answered Aug 28, 2016 at 7:49

Mykola Borysyuk

3,4211 gold badge22 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Андрей _-_ Over a year ago

getting "call back is not a function"

Mykola Borysyuk Over a year ago

You sure that you run as we told you.. Callback it's just a name of callback function. All should work if you copy code directly. Look at runQuery example

Mykola Borysyuk Over a year ago

I even simplify a little bit more.

Mykola Borysyuk Over a year ago

Let us continue this discussion in chat.

Jagdish Idhate · Accepted Answer · 2016-08-28 07:47:56Z

MongoClient.connect & collection.find are asynchronous functions. To get value of resp properly you can make getData function asynchronous as below.

function getData(table, where, to_select, callback) { // We pass callback function 
    var r = {};
    MongoClient.connect("mongodb://127.0.0.1:27017/db", function(err, db) {
        if (!err) {
            collection = db.collection(table);
            collection.find(where, to_select).toArray(function(err, resp) {
             // r.t = resp; no need to assign as you want resp only
             callback(err,resp); // return resp
            })
        }else
           callback(err);// return with error 
    });
    //return r.t; r.t will be undefined as r.t is not updated yet, so we can remove this
}


/*Now you can call as below
  getData(whatever,)whatever,whatever,function(err,resp){
      console.log(resp);// You will get result here
  })*/

Collectives™ on Stack Overflow

use string out of a mongodb function

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related