Cool DB stuff

channel.rb

        def add_user_access(user, *flags_to_add)
            # normalize arguments into a form we'll recognize
            flags_to_add.collect! { |flag| flag.to_sym }
            id = user.to_i

            # backup our arguments in case we need to restore to them later
            flags = user_flags(id)
            flags_backup = flags.dup
            flag_lookup_backup = {}
            flags_to_add.each do |flag|
                flag_lookup_backup[flag] = flag_users(flag).dup
            end

            begin
                $db.transaction do
                    flags_to_add.each do |flag|
                        # don't bother adding a flag we've already got
                        next if flags.include?(flag.to_sym)

                        # otherwise, make a new ChannelFlag object and set it up
                        channel_user_flag = ChannelUserFlag.new
                        channel_user_flag.channel = self
                        channel_user_flag.user_id = id
                        channel_user_flag.flag    = flag.to_s

                        # add the flags to our cache and the DB
                        flags << flag
                        add_channel_user_flag(channel_user_flag)
                        flag_lookup = flag_users(flag)
                        flag_lookup << id unless flag_lookup.include?(id)
                    end
                end
            rescue Exception => e
                # rollback changes to our cache if we couldn't save
                @user_lookup[id] = flags_backup
                flag_lookup_backup.each do |flag, users|
                    @flag_lookup[flag] = users
                end

                # reraise cause we don't know for sure how to proceed from here
                raise e
            end
        end