has_many validation the Rails way

Okay, this is something I run into a lot and don't really have a great
solution. Here is a simple example:

class Blog < ActiveRecord::Base
  has_many :posts
  validates_presence_of :name
end

class Post < ActiveRecord::Base
  belongs_to :blog
  validates_presence_of :name
  validates_presence_of :blog_id
end

Now, if I want to create a blog and post at the same time I don't want
either to be created if one of them fails. So imagine that I have a
new valid blog, but a post with no name. I do not want the blog to be
created because the post failed validation.

Thanks,
Tom

Is this the multiple-models-one-form problem? If so, see this & the prior 2 railscasts:

http://railscasts.com/episodes/75-complex-forms-part-3

The problem that's not treated in those (IIRC) is how to give informative error messages when child item validation fails. IIRC, you get *something* but it's not super informative...

HTH,

-Roy

Roy,

I have probably 3 different solutions I've used in different places,
but they each have different drawbacks. The closest solution is the
one you refer to, where when the child validates it has an error on
the required parent_id, but the parent_id is only missing because the
child failed validation!

Any beautiful solutions out there?

Thanks,
Tom