comment.js

var Schema = require('mongoose').Schema,
	ObjectId = Schema.ObjectId,
	Transaction = require('./transaction.js');

var Comment = module.exports = new Schema({	
	'author': String,
	'body': String,
	'date': Date,
	
	'parent': ObjectId,
	
	'score': {'type': Number, 'default': 0},
	'transactions': [Transaction]
});

gistfile1.js

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
TypeError: Cannot read property 'states' of undefined
    at EmbeddedDocument.isDirectModified (/home/mappum/aptt/node_modules/mongoose/lib/document.js:673:36)
    at EmbeddedDocument.set (/home/mappum/aptt/node_modules/mongoose/lib/document.js:417:17)
    at EmbeddedDocument.parent (/home/mappum/aptt/node_modules/mongoose/lib/document.js:993:45)
    at EmbeddedDocument.EmbeddedDocument (/home/mappum/aptt/node_modules/mongoose/lib/types/embedded.js:19:15)
    at new EmbeddedDocument (/home/mappum/aptt/node_modules/mongoose/lib/schema/documentarray.js:26:17)
    at DocumentArray.SchemaArray (/home/mappum/aptt/node_modules/mongoose/lib/schema/array.js:48:19)
    at new DocumentArray (/home/mappum/aptt/node_modules/mongoose/lib/schema/documentarray.js:42:13)
    at Function.interpretAsType (/home/mappum/aptt/node_modules/mongoose/lib/schema.js:220:14)
    at Schema.path (/home/mappum/aptt/node_modules/mongoose/lib/schema.js:185:29)
    at Schema.add (/home/mappum/aptt/node_modules/mongoose/lib/schema.js:121:12)

item.js

var mongoose = require('mongoose'),
	schema = require('./schemas/item.js');

module.exports = mongoose.model('Item', schema);

schemas.item.js

var Schema = require('mongoose').Schema,
	Comment = require('./comment.js'),
	Transaction = require('./transaction.js');

var Item = module.exports = new Schema({
	'title': String,
	'author': String,
	'body': String,
	'link': String,
	'class': {'type': String, 'lowercase': true}, // the type of post (e.g 'youtube', 'text')
	'tags': {'type': [String], 'index': true},
	'date': {'type': Date, 'default': Date.now},
	
	'comments': [Comment],
	
	'score': {'type': Number, 'default': 0},
	'transactions': [Transaction]
});

var Schema = require('mongoose').Schema,
    ObjectId = Schema.ObjectId,
    Transaction = require('./transaction.js');

var Comment = module.exports = new Schema({ 
    author: {type: String},
    body: {type: String},
    date: {type: Date},

    parent: {type: ObjectId},

    score: {type: Number, 'default': 0},
    transactions: [{type: ObjectId, ref: 'Transaction'}]
});