##实例方法

　　有的时候，我们创造的Schema不仅要为后面的Model和Entity提供公共的属性，还要提供公共的方法.那怎么在Schema下创建一个实例方法呢，请看示例：

var mongoose = require('mongoose');
var saySchema = new mongoose.Schema({name : String});
saySchema.method('say', function () {
  console.log('Trouble Is A Friend');
})
var say = mongoose.model('say', saySchema);
var lenka = new say();
lenka.say(); //Trouble Is A Friend