Rails - Jan 2007 - Validating that a record in a related table exists

Hi, I''m fairly new to Ruby and Rails.  I''m trying to get my
models
validating and I''ve run into a problem.

I''ve got two models User and Contact.  User belongs_to contact and
contact has_one user.

A Contact can exist without a User, however a User cannot exist without
a corresponding Contact.

Also, the Contact model contains an email address.  This email address
can be null, but if there is a User corresponding with the Contact then
there must be an email address.

So basically, upon creating a user I need to check that (a) the
contact_id of the user exists in Contacts, and (b) that the email field
of the corresponding Contact is not blank.

Is there a special Rails way of doing this (particularly part a), or do
I need to create my own validation code (which I assume will be the case
for part b no matter what)?

Also, am I right in assuming that if I use contact.email within an
instance of my User class it will pick out the corresponding Contact for
said User?

Thanks for any help or pointers!

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Okay, I think I''ve got it:

I''ve put in the User model "validates_presence_of :contact"
to ensure
that the contact actually exists.

I''ve then added the following validates method:

  def validate
    if contact && contact.email.nil?
      errors.add(''email'', ''Related contact must have
email'')
    end
  end

Testing seems to work so I think it''s right!


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