mg_model.js

 Model.define('User',{

   collection : 'test_user', // (optional) if not present uses the model name instead.

   // defines your data structure
   types: {
     _id : Object, // if not defined, Mongoose automatically defines for you.
     username: String,
     first : String,
     last : String,
     bio: {
       age: Number
     }
   },

   indexes : [
     'username',
     'bio.age',
     [['first'],['last']] // compound key indexes
   ],

   static : {}, // adds methods onto the Model.
   methods : {}, // adds methods to Model instances.

   setters: { // custom setters
     first: function(v){
       return v.toUpperCase();
     }
   },

   getters: { // custom getters
     username: function(v){
       return v.toUpperCase();
     },

     legalDrinkingAge : function(){
       return (this.bio.age >= 21) ? true : false;
     },

     first_last : function(){ // custom getter that merges two getters together.
       return this.first + ' ' + this.last;
     }
   }
 });

use_model.js

Mongoose.load('./models/');

User = Mongoose.get('User');

user = new User({username : 'test', first : 'me', last : 'why', bio : { age : 100 }}); // create a new document.
user.save(); //save
user.first_last // returns 'ME why'
user.legalDrinkingAge // true

// you can set new properties that aren't defined on the model
user.new_property = 'test';  
user.save();