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

If you're using Rails 2.3 you are using the new nested model stuff. I have noticed the same failures with validates_presence_of as you pointed out, or if :null => false was specified in the migration for that field.

If your intent is to create nested models, you should add accepts_nested_attributes_for :comments to article.rb. This would allow you to:

a = Article.new
a.comments_attributes = [{:body => "test"}]
a.save!  # creates a new Article and a new Comment with a body of "test"

What you have is the way it should work to me, but I'm seeing that it doesn't with Rails 2.3.2. I debugged a before_create in comment using your code and no article_id is supplied through the build (it is nil) so this is not going to work. You'd need to save the Article first as Nicholas pointed out, or remove validation.