Given a HABTM relationship, for example between Products and Categories, is it appropriate to add a validation such as the following? # product.rb validates :categories, :presence => true This works for me. If there''s not at least one associated category then validation fails, and if there is then it passes. However I''m wondering if it''s correct or if there might be unintended consequences, especially because I can''t find examples of this usage anywhere. What do people most commonly do in this situation? I know I can write a custom validation method, but since this seems to work... -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.