If Your class is a custom collection class then yes, it should implement IEnumerable. In this case a public property for the inner list would be redundant. Imagine a simple class: What this code is saying is that if userId was specified, then add a filter on the data so https://cobjectkullanm53950.sunderwiki.com/786021/c_ienumerable_nasıl_kullanılır_aptallar_için