title: Custom constructor function in Mongoose schema/models
body: <p>Greeting all!</p>
  
  <p>I defined a Mongoose schema as below and registered a model (InventoryItemModel). Is there a way to create a custom constructor function for the schema, so that when I instantiate an object from the model, the function will be called (for example, to load the object with value from database)?</p>
  
  <pre><code>var mongoose = require('mongoose')
    , Schema = mongoose.Schema
  
  var InventoryItemSchema = new Schema({
      Sku : String
    , Quanity : Number
    , Description : String
    , Carted : []
    , CreatedDate  : {type : Date, default : Date.now}
    , ModifiedDate  : {type : Date, default : Date.now}
  });
  
  mongoose.model('InventoryItem', InventoryItemSchema);
  
  var item = new InventoryItem();
  </code></pre>
  
  <p>Can I add some custom constructor function so that the item will be populated from database upon instantiation?</p>