title: Mongo db query find doesn't show array result
body: <p>I'm new to node js / Express development. I have developed a login service that works fine. Now i need to upgrade this service and using the username of login to do a query on other mongo document and retrieve an  array result into json message
  I have write a query using findOne, and works, but if i use query find the array is empty</p>
  
  <pre><code>router.post('/login', function(req, res) {
  User.findOne({ username: req.body.username}, function(err, user) {
      if (err){
          return res.status(500).send('Error on the server.');
      }
      if (!user){
          return res.status(401).send({status: 'ko', error: {msg: 'The username ' + req.body.username + ' is not associated with any account.'}});
      }
      var passwordIsValid = bcrypt.compareSync(req.body.password, user.password);
      //if (!passwordIsValid) return res.status(401).send({ auth: false, token: null });
      if (!passwordIsValid){
          return res.status(401).send({status: 'ko', error: {msg:'Authentication failed. Wrong password.',auth: false, token: null}});
      }
      // Make sure the user has been verified
      if (!user.isVerified){
          return res.status(401).send({status: 'ko', error: {type: 'not-verified', msg: 'Your account has not been verified.'}});
      }
      if (!user.statusUser){
          return res.status(401).send({status: 'ko', error: {msg: 'The username ' + req.body.username + ' is blocked by Admin'}});
      }
      // if user is found and password is valid
      // create a token
      var token = jwt.sign({ id: user._id }, config.secret, {
        expiresIn: 86400 // expires in 24 hours
      });
  
      // inserimento farm id //
      Farm.find({ farmId: user.farmId}, (err, farms) =&gt; {
          console.log(Farm.find({farmId:user.farmId}));
          var identify_farm = [];
          if (err) {
              //return res.status(400).send({ status: 'ko', data: {msg: err.message }});
              var txt = err.message;
              identify_farm.push(txt);
          }
          if (!farms) {
              //return res.status(404).send({ status: 'ko', data: {msg: 'Farm not found.'}});
              identify_farm.push('Farm not found.');
          }
          if (farms) {
              identify_farm.push(farms._id);
          }
      // inserimento farm id //
  
      // return the information including token as JSON
      req.session.user = user;
      res.status(200).send({status: 'ok', data: {auth: true, token: token, farmId: user.farmId, roles: user.roles, id_utente: user._id, identify_farms: identify_farm}});
      });
  });
  });
  </code></pre>
  
  <p>This is an example of my db:</p>
  
  <pre><code>{
  "_id" : ObjectId("5c1e2586d695741104f724f1"),
  "demographics" : {
      "farmSize" : "100",
      "crops" : "Forage Crops",
      "liveStock" : "YES",
      "precisionFarming" : "YES",
      "currentTire" : "Dealer"
  },
  "farmId" : "mAje06ni",
  "companyName" : "xxxx",
  "firstname" : "xxxxx",
  "address" : "xxxxxx",
  "city" : "Roma",
  "state" : "Italy",
  "postalcode" : "xxxxx",
  "country" : "Italia",
  "telephone" : "xxxxxxxxx",
  "email" : "xxxxxxxxxx",
  "lat" : 41.7476267,
  "lon" : 12.3648812,
  "__v" : 0
  }
  
  /* 4 */
  {
  "_id" : ObjectId("5c1e4f2dbc87ba0730969f07"),
  "demographics" : {
      "farmSize" : "200",
      "crops" : "Forage Crops",
      "liveStock" : "YES",
      "precisionFarming" : "YES",
      "currentTire" : "Special Tire"
  },
  "farmId" : "mAje06ni",
  "companyName" : "xxxxxx",
  "firstname" : "xxxxxx",
  "address" : "xxxxxxxxx",
  "city" : "Roma",
  "state" : "Italy",
  "postalcode" : "00100",
  "country" : "Italy",
  "telephone" : "xxxxxx",
  "email" : "xxxxxxxxxxxxxx",
  "timestamp" : ISODate("2018-10-16T16:00:00.000Z"),
  "lat" : 41.752784,
  "lon" : 12.368663,
  "__v" : 0
  }
  </code></pre>
  
  <p>I need array result into identify_farms. Why my result is empty?
  Thanks</p>