为什么当我在LINQ to Entities查询中使用GroupBy（）时，结果中的导航属性为null？

Question

Edited:

I'm developing an application with EF code first, I have a method that return a Dictionary<int,T> :

public Dictionary<int, DocumentStationHistory> GetLastDocumentStationHistoryListOfDocuments(string criteria)
{
        Dictionary<int, DocumentStationHistory> result = new Dictionary<int, DocumentStationHistory>();
        using (IUnitOfWork uow = new MyContext())
        {
            DocumentStationHistoryRepository repository = new DocumentStationHistoryRepository(uow);
            result = repository.All().
                Include(x => x.DocumentStation).
                Where(criteria,new object[]{}).
                OrderBy(d=>d.DocumentId).
                OrderBy(d=>d.DocumentStationHistoryId).
                GroupBy(g => (int)g.DocumentId).
                ToDictionary(g => (int)g.Key, g => g.LastOrDefault());
            return result;
        }
}

Also it's the relation between my entities:

But when this method runs, the included property( DocumentStation ) in the result is null . where is my mistake?

Updated:

I tested that if I remove the .GroupBy() , it keeps the navigation property! So how can I solve this problem?

Answer 1

Also had this issue. I solved it by doing a .ToList() before the group by. So it would be:

result = repository.All().
         Include(x => x.DocumentStation).
         Where(criteria,new object[]{}).
         OrderBy(d=>d.DocumentId).
         OrderBy(d=>d.DocumentStationHistoryId).
         ToList().
         GroupBy(g => (int)g.DocumentId).
         ToDictionary(g => (int)g.Key, g => g.LastOrDefault());