I am trying to execute complex OrderBy in Linq, without having to call ToList () first

Question

This works, but requires me to execute the extra .ToList () too early, so it is slow ...

public static Expression<Func<Admission, int?>> CurrentHouseSequence()
{
    return a => a.Person.Locations.OrderByDescending(l => l.TransferDate).DefaultIfEmpty(new Location()).Select(s => s.House != null ? s.House.Seq : null).FirstOrDefault();
}

var getCurrentHouseSequence = AdmissionRoot.CurrentHouseSequence().Compile();

List<Admission> adms = Db.Admissions
    .ToList() //done to prevent CurrentHouseSequence causing run time linq exception.
    .OrderBy( a => getCurrentHouseSequence(a)) 
    .Take(100)
    .ToList();

Then I tried the following: insert the extracted source link from the function directly into orderby, but get an exception at runtime

An object or complex type 'DataContext.Location' cannot be constructed in a LINQ to Entities query.

List<Admission> adms = Db.Admissions
    .OrderBy( a => a.Person.Locations.OrderByDescending(l => l.TransferDate).DefaultIfEmpty(new Location()).Select(s => s.House != null ? s.House.Seq : null).FirstOrDefault())
    .Take(100)
    .ToList();

... Does anyone have any ideas how this can be achieved, please ???

so that was my final decision (thanks to Rob) ...

List<Admission> adms = Db.Admissions
    .OrderBy(a => a.Person.Locations.Any() 
        ? a.Person.Locations.OrderByDescending(l => l.TransferDate)
               .Select(l => l.House != null ? l.House.Seq : null)
               .FirstOrDefault() 
        : null)
    .Take(100)
    .ToList();