Original redeem method

invite.rb

def redeem
  result = nil
  Invite.transaction do
    # Avoid a race condition
    row_count = Invite.update_all('redeemed_at = CURRENT_TIMESTAMP',
                                  ['id = ? AND redeemed_at IS NULL AND created_at >= ?', id, SiteSetting.invite_expiry_days.days.ago])

    if row_count == 1

      # Create the user if we are redeeming the invite and the user doesn't exist
      result = User.where(email: email).first
      result ||= User.create_for_email(email, trust_level: SiteSetting.default_invitee_trust_level)
      result.send_welcome_message = false

      # If there are topic invites for private topics
      topics.private_messages.each do |t|
        t.topic_allowed_users.create(user_id: result.id)
      end

      # Check for other invites by the same email. Don't redeem them, but approve their
      # topics.
      Invite.where('invites.email = ? and invites.id != ?', email, id).includes(:topics).where(topics: { archetype: Archetype::private_message }).each do |i|
        i.topics.each do |t|
          t.topic_allowed_users.create(user_id: result.id)
        end
      end

      if Invite.update_all(['user_id = ?', result.id], ['email = ?', email]) == 1
        result.send_welcome_message = true
      end

      # Notify the invitee
      invited_by.notifications.create(notification_type: Notification.types[:invitee_accepted],
                                      data: { display_username: result.username }.to_json)

    else
      # Otherwise return the existing user
      result = User.where(email: email).first
    end
  end

  result
end