Help with linq orderby on class aggregate relationships

public class Comment
{
     public string Message {get; set;}
     public DateTime Created {get; set;}
}

public class Post
{
    public int PostId {get; set;}
    public string Content {get; set;}
    public IList<Comment> Comments {get; set;}
}

var query = from p in _repository.GetPosts()
                        where p.PostId == id
                        orderby p.Comments.Select(x => x.Created)
                        select p;

            return query.Single();

orderby p.Comments.Max(x=>x.Created)

Post post = ...

post.Comments = post.Comments.OrderBy(x=>x.Created).ToList();

post.Comments.Sort((x, y) => (x.Created.CompareTo(y.Created)));

post.Comments.Sort(x=>x.Created);

public static void Sort<TSource, TKey>(
    this List<TSource> source,
    Func<TSource, TKey> selector)
{
    var comparer = Comparer<TKey>.Default;
    source.Sort((x, y) => comparer.Compare(selector(x), selector(y)));
}

p.Comments.Select(x => x.Created)

p.Comments.Max(x => x.Created)

var query = from p in _repository.GetPosts()
                    where p.PostId == id
                    orderby {
                        Comment comment = p.Comments.FirstOrDefault();
                        return comment == null ? DateTime.MinValue : comment.Created;
                    }
                    select p;

p.Comments = p.Comments.OrderBy(x => x.Created).ToList();

var query = from p in _repository.GetPosts()
            where p.PostId == id
            orderby p.Comments.Select(x => x.Created)
            select p;

var ret = query.Single();
ret.Comments = ret.Comments.OrderBy(x => x.Created).ToList();
return ret;