https://mongodb.github.io/mongo-csharp-driver/2.12/apidocs/html/M_MongoDB_Driver_Linq_MongoQueryable_GroupJoin__4.htm
MongoQueryable.GroupJoin(TOuter, TInner, TKey, TResult) Method (IMongoQueryable(TOuter),...
Correlates the elements of two sequences based on key equality and groups the results.
tkeymethod
https://learn.microsoft.com/id-id/dotnet/api/system.linq.enumerable.groupjoin?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
Enumerable.GroupJoin Method (System.Linq) | Microsoft Learn
Correlates the elements of two sequences based on key equality, and groups the results.
enumerablemethodsystemlinqmicrosoft