In the previous blog post we used a navigational property to work around the limitations of the extension method GroupBy. The problem is, there is not always such a property we can use for grouping. Especially, when following domain driven design practices, a bidirectional navigation is undesirable to not to pollute the domain model (too much). Besides not introducing a navigational property intentionally there might be use cases when we have to group data by property such as the name of a record. In this case there simply cannot be a navigational property.