search for: some_invalid_id

..._to :author validates_associated :author But I DON''T have validates_presence_of. What I want to do is validate that an author is valid --if it is specified--. + I want to allow for the case where article.author_id = nil. + I DO NOT want to allow for the case where article.author_id = SOME_INVALID_ID During testing, I tried this: article = Article.new article.author_id = nil assert c.valid? (True -- working so far) article.author_id = 5 assert c.valid? (True -- because author 5 is valid) article.author_id = 999 assert c.valid? (True!?! -- shouldn'...