How do I validate that two values do not equal each other in a Rails model?

Question

I have a User model, which has an email and a password field. For security, these may not be equal to each other. How can I define this in my model?

Answer 1

It depends how Your password is stored:

class User < ActiveRecord::Base
    validate :email_and_password_validation

    def email_and_password_validation
        if self.email == self.password
            errors.add_to_base("Password must be different from email") 
        end
    end
end

This would work if Your password is stored literally, but You can perform the same thing with email (e.g. create a hashed version) and check for equality with password. E.g:

class User < ActiveRecord::Base
    validate :email_and_password_validation

    def email_and_password_validation
        if make_hash(self.email) == self.hashed_password
            errors.add_to_base("Password must be different from email") 
        end
    end
end

My example is taken from http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#M002162

Your situation is quite general so You can be interested in creating custom validation method. Everything is covered here: http://guides.rubyonrails.org/active_record_validations_callbacks.html#creating-custom-validation-methods