Sort LINQ query by child collection's child property?

Question

I have these objects: ``` public class Class { public Guid Id {get;set;} public string Name {get;set;} public virtual ICollection<Schedule> Schedules{get;set;} } public class Schedule { public Guid Id {get;set;} public virtual DayOfTheWeekId {get;set;} public virtual DayOfTheWeek {get;set;} public DateTime StartTime {get;set;} public DateTime EndTime {get;set;} } ``` My current query looks like this, but I get this exception: At least one object must implement IComparable.: ``` Repository .Get(c => c.Schedules.Any(s => s.DayOfTheWeekTypeId == dayOfTheWeekId)) .OrderBy(e => e.Schedules.OrderBy(s => s.StartDateTime)).ToList() ``` when I set the times i always use the same day, because I need to show classes on certain days of the week. That is where the DayOfTheWeek object comes into play. This is how I am setting the times: ``` var schedule = new Schedule{ StartDateTime = new DateTime(1999,1,1) + new TimeSpan(9, 15, 0), EndDateTime = new DateTime(1999,1,1) + new TimeSpan(9, 15, 0), Day…

Accepted Answer

You're trying to order by a sequence. What does that even mean?

It would make more sense to order by - say - the earliest event in the schedule:

```
.OrderBy(e => e.Schedules.Min(s => s.StartDateTime))
```

I don't know whether that will work, but it at least makes more sense. (It would work in LINQ to Objects. I have no idea about EF though.)

Sort LINQ query by child collection's child property?

Solution

Problem