How can you validate the presence of a belongs to association with Rails?

Question

Say I have a basic Rails app with a basic one-to-many relationship where each comment belongs to an article:

$ rails blog
$ cd blog
$ script/generate model a         


        

Answer 1

This fails because there is no identity map in Rails 2.3 or 3.0. You can manually fix it by stitching them together.

a = Article.new
c = a.comments.build
c.article = a
a.save!

This is horrible, and what the identity map in 3.1 will help to fix (in addition to performance gains). c.article and a.comments.first.article are different objects without an identity map.