If An airline is "countable", this means that there MUST be a flight attendant present on the plane, whose sole job is to count: What this code is saying is that if userId was specified, then add a filter on the veri so that only items where the userId matches https://lanekyisz.mdkblog.com/33689127/c-ienumerable-nasıl-kullanılır-ile-ilgili-detaylı-notlar