Rails, polymorphic association - find records with non-dead associated records

Question

I have following Comments-on-Models design (source: http://railscasts.com/episodes/154-polymorphic-association): class Comment belongs_to :commentable, :polymorphic => true end class Post has_many :comments, as => :commentable end class Message has_many :comments, :as => :commentable end etc... How can I select all records from 'comments' table, so that each record has non-dead commentable (dead means original fx Post was deleted) by scope-based query? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

Since commentable not exists in case of dead-commentable, you can do something like this: class Comment belongs_to :commentable, :polymorphic => true scope :non_dead_commentable, where('commentable IS NOT NULL') end In rails 4 you can do: scope :non_dead_commentable, where.not(:commentable => nil) And then: Comment.non_dead_commentable