Conditional Statements In Ruby on Rails Model File

Is it possible for us to write conditional statements in our Rails model file for example in my case if I want to implement some validations based on if a user is singned_in or not in my Customer.rb file.

if user_signed_in?  // if signed_in is true
     //my validation code here

then some special validations and

else !user_signed_in? // if signed_in is false
     //my validation code here