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

You are correct. The article needs an id before this validation will work. One way around this is the save the article, like so:

>> article = Article.new
=> #

>> article.save!
=> true
>> article.comments.build
=> #
>> article.save!
=> true

If you are creating a new article with a comment in one method or action then I would recommend creating the article and saving it, then creating the comment, but wrapping the entire thing inside of a Article.transaction block so that you don't end up with any extra articles.