Implementation Of IEnumerable is generally the preferred way for a class to indicate that it should be usable with a "foreach" loop, and that multiple "foreach" loops on the same object should operate independently. What this code is saying is that if userId was specified, then add a filter on https://trevorkyhqy.activosblog.com/27531154/5-temel-unsurları-için-c-ienumerable-kullanımı