ruby on rails - Validate uniqueness of a field scoped with :through association -


there 3 models: talk, topic , conference. each have title , description. conference has many topics , topic has many talks.

class conference < applicationrecord     has_many :topics     has_many :talks, through: topics end  class topic < applicationrecord     belongs_to :conference     has_many :talks end  class talk < applicationrecord     belongs_to :topic     belongs_to :conference, through: :topic end

how validate talk has unique title within conference?

the solution come create table talk-topic association , perform validation there. can achieved without creating new table?

try this

validate :unique_talk_in_conference def unique_talk_in_conference    if self.conference.talks.collect(&:title).include?(self.title)        errors.add(:title, "talks should unique in conference")    end end

p.s: didn't test it


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