how to set custom setter for property in mongoose js?

how do i define setter for schema property after I have defended schema like

var User=new Schema({email:String})

now how do I define setter for that email property like User.email.setter(function ...) ???

Thanks

I found the solution.....custom properties can be set like

User.path("email",{
        set:function(email){
           return email
        }
    })