Because Devise 3 (and/or Warden) changed the signature of the session info, all sessions were invalidated and thereby people logged out. You do *not* log people out unless they ask for it. Capisce? This migration migrates migraines by migrating those sessions. Replace the word "account" and "Account" if your account model isn't named Account, bu…

migrate_sessions_to_devise_3.rb

class MigrateSessionsToDevise3 < ActiveRecord::Migration
  class Session < ActiveRecord::Base
    attr_protected
    serialize :data, JSON
  end

  def up
    Session.find_each do |session|
      warden = session.data["warden.user.account.key"]
      next unless warden
      next unless warden[0] == "Account"

      warden.shift 
      session.data["warden.user.account.key"] = warden
      session.update_column(:data, JSON.dump(session.data))
    end
  end

  def down
    Session.find_each do |session|
      warden = session.data["warden.user.account.key"]
      next unless warden
      next if warden[0] == "Account"

      warden.unshift "Account"
      session.data["warden.user.account.key"] = warden
      session.update_column(:data, JSON.dump(session.data))
    end
  end
end