Question

I am getting a little confused and need some help please. Take these two classes

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;} } 

I want to write a linq query which returns a single Post but ordered by the comment created date.

So i started off constructing my linq query as follows:

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

But the orderby statement seem not to work! It just returns my list in the default sort order. Any suggestions on how i can make this work??? Thanks in advance!

Answer 1

Ordered by which comment date? the first? the last? You cuold try:

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

for example.

Also – your Single suggests you expect exactly one row, in which case there isn’t much point sorting it. Do you mean First() ?

---

Or do you mean that you want to sort the Comments? In which case, get the Post first;

Post post = ... 

Now… sorting the Comments is a little tricky because of your IList<T> – if you don’t mind it being a little inefficient, this is simple:

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

Of course, if the Comments was List<T>, you could do:

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

There are also tricks you can do to make an extension method of the form:

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

i.e.

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))); }