Proper way to validate password

Question

I have a user registration page. I want user password to be from 4 to 16 symbols. I need to check that they have at least one uppercase letter and 1 digit. Than I am making md5 hash of this password and put it into database.
How do I validate it?
Validation in model tests if password is 32symbols length:

  validates :password, :length => { :minimum => 32 , 
            :message => 'Not an md5 password provided.' }

But how do I validate that password matches my requirements before making a hash of it and set appropriate errors for this validation?
I would like view to get user.errors[:password] containing something like 'Must have at least one digit.' and 'Must have at least one uppercase letter.'

Answer 1

You can create a custom validator method where you can do whatever you want:

validate :password_validation

def password_validation
  unless password.length > 32 && ... # other requirements
    errors.add(:password, 'Not an md5 password provided.')
  end
end

Answer 2

You can provide custom callbacks. See this link from the Rails guide: http://guides.rubyonrails.org/active_record_validations_callbacks.html#custom-validators