how to find model objects that belong to more than one model object

Question

Suppose I have the models Book and Reading, which has the relationship Book has_many :readings.

Now suppose I want to find all books that have been read in the past week. I know I can find readings created in the past week with something like: readings = Reading.find(:all, :conditions => ["created_at > ?", Date.today - 7])

However, I'm not sure how to get from that list of readings to a de-duplicated list of books. I know I can't simply do readings.books because readings is an array and Array#books is not defined.

Any help would be appreciated.

Answer 1

Book.joins(:readings).group(:book_id).having("COUNT(*) > 1")