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

If you want to support multiple languages, you have to come up with another solution, which translates the error messages and the attribute names. So I created a new each validator for that.

validators/values_not_equal_validator.rb:

class ValuesNotEqualValidator < ActiveModel::EachValidator
  def validate(record)
    @past = Hash.new
    super
  end

  def validate_each(record, attribute, value)
    @past.each do |k, v|
      if v == value
        record.errors.add(attribute, I18n.t('errors.messages.should_not_be_equal_to') + " " + record.class.human_attribute_name(k))
      end
    end
    @past[attribute] = value
  end
end

I call it in the model like this:

class User < ActiveRecord::Base
  validates :forename, :surname, values_not_equal: true
end

And I translate it the messages like this:

de:
  activerecord:
    attributes:
      user:
        forename: 'Vorname'
        surname: 'Nachname'
  errors:
    messages:
      should_not_be_equal_to: 'darf nicht gleich sein wie'