CODEWITHSUNDEEP
c#.netlinq
Raph
Raph

Reputation: 384

Linq OrderBy aggregates dates

I would like to order a list of posts by date of last comment or date of the post.

This is the classes :

public class Post
{    
    public int Id { get; set; }
    public string Text { get; set; }
    public System.DateTime DatePosted { get; set; }
    public ICollection<Comment> Comments { get; set; }
}

public partial class Comment
{
    public int Id { get; set; }
    public int PostId { get; set; }
    public string Text { get; set; }
    public System.DateTime DateCommented { get; set; }
}

The ideal code (whitch don't even compile) would be : 

IEnumerable <Post> posts = MVPMetroEntities.Posts
                                               .OrderByDescending(p => 
                                                       p.DatePosted || p.Comments.Max(c=>c.DateCommented));

Any ideas ? thanks

Upvotes: 1

Views: 229

Answers (4)

Raph
Raph

Reputation: 384

I found the answer, with using ternary operator in the OrderByDescending. Thanks :)

MVPMetroEntities.Posts
            .OrderByDescending(
                    e => e.Comments.Any() ? e.Comments.Max(f => f.DateCommented) : e.DatePosted)

Upvotes: 0

NinjaNye
NinjaNye

Reputation: 7126

var posts = MVPMetroEntities.Posts
                .Select(p => new { 
                     Date = p.Comments.Any() 
                                ? p.Comments.OrderByDescending(c => c.DateCommented).First().Date 
                                : p.DatePosted, 
                     Post = p
                  }
                .OrderByDescending(x => x.Date);

Upvotes: 1

Nasmi Sabeer
Nasmi Sabeer

Reputation: 1380

I didn't understand your intention clearly, but how about this

MVPMetroEntities.Posts
.OrderByDescending(p => Recent(p.DatePosted, p.Comments.Max(c => c.DateCommented)));

by using a helper method/extension methods like this 

        public DateTime Recent(DateTime dt1, DateTime dt2)
        {
            return dt1 > dt2 ? dt1 : dt2;
        }

Note: helper may not work if you are using any ORM like Linq-to-sql

Upvotes: 0

Tim Schmelter
Tim Schmelter

Reputation: 460068

I assume you are looking for ThenByDescending:

IEnumerable<Post> posts = MVPMetroEntities.Posts
    .OrderByDescending(p => p.DatePosted)
    .ThenByDescending(p => p.Comments.Max(c => c.DateCommented));

Upvotes: 2

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