Question

according to rails’ built-in validation functions, what is the difference between these following two methods?

validates :password, :confirmation =>true

and

validates_confirmation_of :password

as far as I understand, the first was just introduced in rails version 3?
am I correct?

Answer 1

They both do the same exact thing, validates_confirmation_of is just one of the many short form helper methods for validates.

If you look at the source, you can see that the validates method is just written to handle all validators whereas validates_confirmation_of explicitly uses the ConfirmationValidator

I think validates_confirmation_of was introduced in Rails 2 so it’s been around for quite a while.

Source comparison:

  def validates_confirmation_of(*attr_names)
    validates_with ConfirmationValidator, _merge_attributes(attr_names)
  end

and

  def validates(*attributes)
    defaults = attributes.extract_options!
    validations = defaults.slice!(*_validates_default_keys)

    raise ArgumentError, "You need to supply at least one attribute" if attributes.empty?
    raise ArgumentError, "You need to supply at least one validation" if validations.empty?

    defaults.merge!(:attributes => attributes)

    validations.each do |key, options|
      # LOOK AT THIS LINE
      key = "#{key.to_s.camelize}Validator"

      begin
        validator = key.include?('::') ? key.constantize : const_get(key)
      rescue NameError
        raise ArgumentError, "Unknown validator: '#{key}'"
      end

      # AND LOOK AT THIS LINE
      validates_with(validator, defaults.merge(_parse_validates_options(options)))
    end
  end