mongoose problems

learn.js

//deps
var mongoose = require( 'mongoose' );
var Schema = mongoose.Schema;
var ObjectId = mongoose.Schema.ObjectId;

//config
var mongo = require( './../conf.js' ).mongo ;
mongo.database = 'learn';

//connect to mongo
var connString = 'mongodb://'+mongo.host+':'+mongo.port+'/'+mongo.database ;
var conn = mongoose.connect( connString );

//recursive embedded-document schema
var Comment = new Schema();
Comment.add({
	title: { type: String, index: true },
	date: Date,
	body: String,
	comments: [Comment]
});

var BlogPost = new Schema({
	title: { type: String, index: true, unique: true },
	slug: { type: String, lowercase: true, trim: true },
	date: { type: Date, default: Date.now },
	buf: Buffer,
	comments: [Comment],
	creator: Schema.ObjectId
});

var Person = new Schema({
	name: {
		first: String,
		last: String
	},
	email: { type: String, required: true, index: {unique: true, sparse: true } },
	alive: Boolean
});

// accessing a schema type by key - !! NOT really working
BlogPost
	.path( 'date' )
	.default( function(){	
		return new Date();
	})
	.set( function(v){
		return v === 'now' ? new Date() : v ;
	});


// pre hook
var emailAuthor = function( done ){
	console.log( '\nemailing author!\n' );
	done();
};
BlogPost.pre( 'save', function( next, done ){
	//next( new Error('something went wrong') );
	next();
});
BlogPost.pre( 'save', function( next, done ){
	//use done() to call stuff from async functions
	emailAuthor( done );
	next(); 
});

//methods
BlogPost.methods.findCreator = function( callback ){
	return this.db.model( 'Person' )
		.findById( this.creator, callback );
};

BlogPost.statics.findByTitle = function( title, callback ){
	return this.find({ title: title }, callback );
};

BlogPost.methods.expressiveQuery = function( creator, date, callback ){
	return this
		.find( 'creator', creator )
		.where( 'data' )
		.gte( date )
		.run( callback );
};

//plugin
var slugGenerator = function( options ){
	options = options || {};
	var key = options.key || 'title';

	return function slugGenerator( schema ){
		schema.path( key ).set( function( v ){
			this.slug = v
				.toLowerCase()
				.replace( /[^a-z0-9]/g, '' )
				.replace( /-+/g, '' );
			return v ;
		});
	};
};
BlogPost.plugin( slugGenerator() );

//define models
mongoose.model( 'BlogPost', BlogPost );
mongoose.model( 'Person', Person );

//tests
var BlogPostModel = mongoose.model( 'BlogPost' );
var instance = new BlogPostModel();
instance.title = 'alex' ;
instance.save( function( err ){
	console.log( 'run save callback' );
	// only use this in case of an error
	if( err ) {
		console.log( 'there was an error' );
	}
	else{
		console.log( 'no error' );
	}
});