Mongoose findById CastError: Cast to ObjectId failed for value at path “_id”

[Ali Reza]

I have simple app , i am usign mongoose for saving data on mongodb

also i am usign autoIncrement for creating mongodb auto increment id. here is my code :

var mongoose = require('mongoose');
var autoIncrement = require('mongoose-auto-increment');

        var connection = mongoose.connect('mongodb://localhost/mymusic', function(err) {

  if(err) {

      console.log('connection error', err);

  } else {

    console.log('connection successful');

    }

});

var Schema = mongoose.Schema;

autoIncrement.initialize(connection);

var singerSchema = new Schema({

          artist_name:  { type : String ,index: true, unique : true },

          artist_id:  { type : String },

          poster:  { type : String },

          created: { type: Date, default: Date.now },

          path: { type : String }

        });

singerSchema.plugin(autoIncrement.plugin, 'singer');

        var singer = mongoose.model('singer', singerSchema);

     var akon = new singer({

      artist_name:'Akon',

      artist_id:150,

      poster:'akon.jpg',

      path: 'akon'

     });

     // Save Singers

     akon.save(function(err){

        if(err)

        console.log(err);

        else

        console.log(fed);

     });

now when i want query by _id :

   

singer.find({ _id: 608 }, function(err, singer) {   
  if (err) throw err;

      // show the one user

      console.log(singer);

    });

i get this error :

CastError: Cast to ObjectId failed for value "608" at path "_id"   

at ObjectId.cast (/home/app/node_modules/mongoose/lib/schema/objectid.js:132:13)

    at ObjectId.castForQuery (/home/app/node_modules/mongoose/lib/schema/objectid.js:182:17)

    at module.exports (/home/app/node_modules/mongoose/lib/cast.js:202:32)

    at Query.cast (/home/app/node_modules/mongoose/lib/query.js:2334:10)

    at Query.find (/home/app/node_modules/mongoose/lib/query.js:995:10)

    at Function.find (/home/app/node_modules/mongoose/lib/model.js:1023:13)

    at Object.<anonymous> (/home/app/search.js:22:8)

    at Module._compile (module.js:456:26)

    at Object.Module._extensions..js (module.js:474:10)

    at Module.load (module.js:356:32)

Query for other fields works just fine , my problem its just with _id field.