Mongoose 3.6 population example

output

===========
    mongoose version: 3.6.0rc0
========


dbname: testing_populateAdInfinitum

[ { title: 'blog 1',
    author: 
     { _id: 511bde3e3985283f25000004,
       name: 'sally',
       __v: 0,
       friends: 
        [ { _id: 511bde3e3985283f25000001, name: 'mary' },
          { _id: 511bde3e3985283f25000002, name: 'bob' } ] },
    _id: 511bde3e3985283f25000005,
    tags: [ 'fun', 'cool' ],
    __v: 0 },
  { title: 'blog 3',
    author: 
     { _id: 511bde3e3985283f25000003,
       name: 'joe',
       __v: 0,
       friends: 
        [ { _id: 511bde3e3985283f25000001, name: 'mary' },
          { _id: 511bde3e3985283f25000002, name: 'bob' } ] },
    _id: 511bde3e3985283f25000007,
    tags: [ 'fun', 'odd' ],
    __v: 0 } ]

populateAdInfinitum.js

var assert = require('assert')
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = mongoose.Types.ObjectId;

console.log('\n===========');
console.log('    mongoose version: %s', mongoose.version);
console.log('========\n\n');

var dbname = 'testing_populateAdInfinitum';
console.log('dbname: %s', dbname);
mongoose.connect('localhost', dbname);
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});

var user = new Schema({
    name: String
  , friends: [{ type: Schema.ObjectId, ref: 'User' }]
});
var User = mongoose.model('User', user);

var blogpost = Schema({
    title: String
  , tags: [String]
  , author: { type: Schema.ObjectId, ref: 'User' }
})
var BlogPost = mongoose.model('BlogPost', blogpost);

mongoose.connection.on('open', function () {
  var userIds = [new ObjectId, new ObjectId, new ObjectId, new ObjectId];
  var users = [];

  users.push({
      _id: userIds[0]
    , name: 'mary'
    , friends: [userIds[1], userIds[2], userIds[3]]
  });
  users.push({
      _id: userIds[1]
    , name: 'bob'
    , friends: [userIds[0], userIds[2], userIds[3]]
  });
  users.push({
      _id: userIds[2]
    , name: 'joe'
    , friends: [userIds[0], userIds[1], userIds[3]]
  });
  users.push({
      _id: userIds[3]
    , name: 'sally'
    , friends: [userIds[0], userIds[1], userIds[2]]
  });

  User.create(users, function (err, docs) {
    assert.ifError(err);

    var blogposts = [];
    blogposts.push({ title: 'blog 1', tags: ['fun','cool'], author: userIds[3] })
    blogposts.push({ title: 'blog 2', tags: ['cool'], author: userIds[1] })
    blogposts.push({ title: 'blog 3', tags: ['fun','odd'], author: userIds[2] })

    BlogPost.create(blogposts, function (err, docs) {
      assert.ifError(err);

      BlogPost.find({ tags: 'fun' }).lean().populate('author').exec(function (err, docs) {
        assert.ifError(err);

        var opts = {
            path: 'author.friends'
          , select: 'name'
          , options: { limit: 2 }
        }

        BlogPost.populate(docs, opts, function (err, docs) {
          assert.ifError(err);
          console.log();
          console.log(docs);
          done();
        })
      })
    })
  })
});

function done (err) {
  if (err) console.error(err.stack);
  mongoose.connection.db.dropDatabase(function () {
    mongoose.connection.close();
  });
}

actually this is correct. but he forgot the model object which is important.
http://stackoverflow.com/questions/19222520/populate-nested-array-in-mongoose

@aheckmann Please add model: User in https://gist.github.com/aheckmann/4947012#file-populateadinfinitum-js-L69 otherwise this doesn't work as mentioned by @keithics

var addContent= mongoose.Schema({
userId:{type:Number},
contentId:{type:Number,index:{unique:true}},
contentType:{type:String},
contentTitle:{type:String},
description:{type:String},
syncTime:{type:Date ,default:Date.now,required:true},
content:{type:String,contentType:String},
lastViewed:{type:Date,default:Date.now,required:true},
action:{type:String},

                });

var addContent=mongoose.model('addContent',addContent,'addContent');
exports.addContent=addContent;

var user= mongoose.Schema({
userId:{type:Number,index:{unique:true}},
username:{type:String,required:true},
mobile:{type:String ,required:true},
active:{type:Boolean,default:false},
otp:{type:Number},
syncTime:{type:Date ,default:Date.now,required:true},
image:{data:Buffer,contentType:String}

                    });

var User=mongoose.model('User',user,'users');

exports.User=User;

when add content by User it automatically update in User collection ....
how can do this???????