Entity Framework select one of each group by date

Question

I have a table like this (Table name: Posts):

+----+--------------------------+-------+------------+
| id |         content          | type  |    date    |
+         


        

Answer 1

From memory, something like this should do it

var data = context.Posts.GroupBy(p => p.Type)
                        .Select(g => new { 
                                          Type = g.Key, 
                                          Date = g.OrderByDescending(p => p.Date)
                                                  .FirstOrDefault()
                                         }
               

This would give you a new anonymous type, but you can always map it to a class

Answer 2

Or using temporary result and predicate

var tmp = posts.GroupBy(x => x.type).Select(x => new {x.Key, date = x.Max(g => g.date)).ToArray();

var filter = PredicateBuilder.False<Post>();

foreach (var item in tmp)
{
    filter = filter.Or(x => x.type == item.Key && x.date == item.date);
}

var newestPosts = posts.Where(filter);

Answer 3

I suppose you can group your Posts rows by type and then select first content from descending ordered by date collection of that type

from row in Posts 
group row by row.type 
into g
select new
{       
    Content  = (from row2 in g orderby row2.date descending select row2.content).FirstOrDefault(),
    Type = g.Key
}

Answer 4

If you want to get the whole Posts. You can try this:

var query = Posts.GroupBy(p => p.Type)
                  .Select(g => g.OrderByDescending(p => p.Date)
                                .FirstOrDefault()
                   )