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
class Post < ActiveRecord::Base
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.