Cleaner way to build a "one or the other" validation?

I have an object called dealer. Dealer has two fields dealer_number
and sub_dealer_number. It must have 1 OR the other... but not both.
To validate this I have:

class Dealer < ActiveRecord::Base
  validate :dealer_id?

private
  def dealer_id?
    if number.blank? && sub_number.blank?
      errors.add_to_base("You must specify either a Dealer Number OR a
Sub Dealer Number.")
    elsif (number.length > 0) && (sub_number.length > 0)
        errors.add_to_base("You must specify either a Dealer Number OR
a Sub Dealer Number.")
    end
  end
end

This looks really messy to me. Is there a better way? Thank you for
your thoughts.

I have an object called dealer. Dealer has two fields dealer_number
and sub_dealer_number. It must have 1 OR the other... but not both.
To validate this I have:

Use the Xor operator ( ^ ) ?

Fred

How about:

def validate_dealer_id
  if number.blank? then
    errors.add_to_base("You must specify either a Dealer Number OR a Sub Dealer Number.") if subnumber.blank?
  else
    erros.add_to_base("A dealer can't have both a dealer number AND a sub dealer number") unless subnumber.blank?
  end
end

?

Extra bonus kibbitzing:
- Would it make things any easier to store both those
   numbers in a single field, and keep track of whether
   a given dealer is a dealer or a sub in a separate 'dealer_type'
   field?
- FWIW--the ruby convention is that methods whose names
   end in a ? return a boolean.

Cheers,

-Roy

Frederick Cheung wrote:

Use the Xor operator ( ^ ) ?

Fred

Sexy. Thanks.

I changed above to:

class Dealer < ActiveRecord::Base
  validate :dealer_id?

private
  def dealer_id?
    if !(number.blank? ^ sub_number.blank?)
      errors.add_to_base("You must specify either a Dealer Number OR a
Sub Dealer Number.")
    end
  end
end

Makes me feel less dirty.

Roy Pardee wrote:

How about:

def validate_dealer_id
  if number.blank? then
    errors.add_to_base("You must specify either a Dealer Number OR a Sub
Dealer Number.") if subnumber.blank?
  else
    erros.add_to_base("A dealer can't have both a dealer number AND a
sub dealer number") unless subnumber.blank?
  end
end

?

Extra bonus kibbitzing:
- Would it make things any easier to store both those
   numbers in a single field, and keep track of whether
   a given dealer is a dealer or a sub in a separate 'dealer_type'
   field?
- FWIW--the ruby convention is that methods whose names
   end in a ? return a boolean.

Cheers,

-Roy

I don't think that your above example is any cleaner then my original
solution. However, your bonus kibbitzing (lol) I think is a really good
thought. I am going to implement this logic on a later iteration.
Thanks for this.

Michael Kahle wrote:

I don't think that your above example is any cleaner then my original
solution. However, your bonus kibbitzing (lol) I think is a really good
thought. I am going to implement this logic on a later iteration.
Thanks for this.

Hi Michael,

For future reference, I needed to do something similar a few months ago
and ended up creating a custom validation. I wrote about it if you want
to look into it:

http://per-snicket-y.blogspot.com/2008/04/custom-validations-in-rails-202.html

Peace.