Lambda query to reverse order a list by date

Question

I have this function that shows a list of messages in reverse order.

 protected void setupMessages(IList<Message> Messages)
 {
     List<Message> messages = new List<Message>() ;
     messages.AddRange( Messages.OrderBy(message => message.DateAdded).Reverse());
     MessagesRepeater.DataSource = messages;
     MessagesRepeater.DataBind();
 }

I was wondering if there was a way to reverse the order within the lambda query without calling the Reverse Method? Or is calling Reverse() the only way to do this?

Answer 1

You simply want to use the OrderByDescending extension method, as opposed to OrderBy.

Indeed, this would be a more efficient method, since it only requires one iteration of the collection rather than two.

messages.AddRange(Messages.OrderByDescending(message => message.DateAdded));

Answer 2

Use OrderByDescending

messages.AddRange( Messages.OrderByDescending( message => message.DateAdded ) );

In fact, you can simplify the whole thing:

protected void setupMessages(IList<Message> Messages)
{     
     MessagesRepeater.DataSource = Messages.OrderByDescending( message => message.DateAdded )
                                           .ToList();
     MessagesRepeater.DataBind();
}