demarches-normaliennes/db/migrate/20170215102943_remove_duplicate_email_received.rb

class RemoveDuplicateEmailReceived < ActiveRecord::Migration[5.0]
  def change
    all_mails = MailReceived.all
     groupped = all_mails.group_by { |m| m.procedure_id }
     filtered = groupped.reject { |k, v| v.length < 2 }
     filtered.each do |k, duplicate_mails|
       duplicate_mails.pop
       duplicate_mails.each(&:destroy)
     end
  end
end