I have 3 models, say A, B and C, and they are set up like this: A: has_many :Bs has_many :Cs, through: B B: belongs_to A: has_many :Cs C: belongs_to B: In my model for C, I want to declare, that a column ccol within C must be unique, but only within the scope of a certain A. If the constraint would require uniqueness within a certain B, I could write validates :ccol, uniqueness: { scope: :B_id } But since C doesn't contain an A_id as foreign key, I can not express it in this way. Is there a possibility to achieve this? Ronald -- Posted via http://www.ruby-forum.com/. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/1c92cfe04af45f69073d2ead29cb3d22%40ruby-forum.com. For more options, visit https://groups.google.com/d/optout.