LINQ Orderby Descending Query

问题

I\'m sure this will be a relatively simple one.

I have a LINQ query that I want to order by the most recently created date.

See:

        var itemList = from t in ctn.Items
                        where !t.Items && t.DeliverySelection
                        orderby t.Delivery.SubmissionDate descending
                        select t;

I have also tried:

       var itemList = (from t in ctn.Items
                        where !t.Items && t.DeliverySelection
                        select t).OrderByDescending();

but this gives an error :

No overload for method \'OrderByDescending\' takes 0 arguments

From what I\'ve read, I\'m fairly sure the first way I\'ve done it should work. I\'ve tried changing descending to ascending just to see if it does anything but it stays the same.

I\'d be grateful if someone could take a look at the query and see if I\'m doing anything wrong. Thanks :)

回答1:

You need to choose a Property to sort by and pass it as a lambda expression to OrderByDescending

like:

.OrderByDescending(x => x.Delivery.SubmissionDate);

Really, though the first version of your LINQ statement should work. Is t.Delivery.SubmissionDate actually populated with valid dates?

回答2:

I think this first failed because you are ordering value which is null. If Delivery is a foreign key associated table then you should include this table first, example below:

var itemList = from t in ctn.Items.Include(x=>x.Delivery)
                    where !t.Items && t.DeliverySelection
                    orderby t.Delivery.SubmissionDate descending
                    select t;

回答3:

I think the second one should be

var itemList = (from t in ctn.Items
                where !t.Items && t.DeliverySelection
                select t).OrderByDescending(c => c.Delivery.SubmissionDate);

回答4:

Just to show it in a different format that I prefer to use for some reason: The first way returns your itemList as an System.Linq.IOrderedQueryable

using(var context = new ItemEntities())
{
    var itemList = context.Items.Where(x => !x.Items && x.DeliverySelection)
                                .OrderByDescending(x => x.Delivery.SubmissionDate);
}

That approach is fine, but if you wanted it straight into a List Object:

var itemList = context.Items.Where(x => !x.Items && x.DeliverySelection)
                                .OrderByDescending(x => x.Delivery.SubmissionDate).ToList();

All you have to do is append a .ToList() call to the end of the Query.

Something to note, off the top of my head I can't recall if the !(not) expression is acceptable in the Where() call.

来源：https://stackoverflow.com/questions/5344805/linq-orderby-descending-query

标签

linq

sql-order-by