The LINQ expression could not be translated when using MaxBy

Question

Entities:

public class User
{
  public long Id { get; }
  public ICollection<File> Files { get; }
}

public class File
{
  public long Id { get; }
  public DateTime CreatedAt { get; }
  public string Name { get; }
  public User? User { get; }   // nullable for other reasons
}

I want the name of the latest file for each user. I tried:

var data = await context
  Files
  .Where(x => x.User != null)
  .GroupBy(x => x.User!.Id)
  .Select(x => x.MaxBy(y => y.CreatedAt)!)
  .ToDictionaryAsync(k => k.User.Id, v => v.Name);

But that throws

The LINQ expression ... could not be translated

I assume MaxBy is unsupported (in EF Core 8).

Is there a workaround?

Answer 1

Thanks to the comment by @PanagiotisKanavos above, the simplest solution is:

await context
  .Users
  .Include(x => x.Files)
  .Where(x => x.Files.Any())
  .ToDictionaryAsync(
    x => x.Id, 
    x => x.Files.OrderByDescending(y => y.CreatedAt).First().Name)

That completely avoids the MaxBy issue.

Vote here for them to support it.