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

Instead of validating the presence of the article's id you could validate the presence of the article.

validates_presence_of :article

Then when you are creating your comment:

article.comments.build :article => article