LINQ - 如何按日期排序

Question

I have the following table (Records):

RecordID int,
Nickname nvarchar(max),
DateAdded datetime

I need group by max count of records for Nickname. I made it:

        var users = (from i in db.Records
                     where i.Form.CompetitionID == cID
                     group i by i.Nickname into g
                     orderby g.Count() descending
                     select new TopUserModel()
                     {
                         Nickname = g.Key,
                         Position = g.Count()
                     }).Take(100).ToList();

it works

Right now I need to sort it by date too (who first got max records). I should have a request like it:

select Nickname, Count(*) as Result, MAX(DateAdded) as MDate from Records group by Nickname order by Result Desc, MDate Asc

How to do it by LINQ?

Answer 1

I think this is what you want. I've used extension version of Linq which is probably more easier. The idea is to calculate MaxCount and MaxDate after GroupBy so you can use it in next OrderBy clauses.

db.Records
.Where(i => i.Form.CompetitionID == cID)
.GroupBy(i => i.Nickname)
.Select(g => new { MaxCount = g.Count(), MaxDate = g.Max(i => i.DateAdded), Nickname = g.Key})
.OrderByDescending(gx => gx.MaxCount)
.ThenByDescending(gx => gx.MaxDate)
.Select(gx => new TopUserModel()
{
     Nickname = gx.Nickname,
     Position = gx.MaxCount
}).Take(100).ToList();

Answer 2

I think what you're asking for is:

...
select new TopUserModel()
{
    Nickname = g.Key,
    Position = g.Count()
    Date = g.Max(r => r.DateAdded)
}).Take(100).OrderByDescending(t => t.Position).ThenBy(t => t.Date).ToList();

When you use group the Key is your grouping but the enumerable is all the records you've grouped so you can still use aggregate functions on them.

If you want to sort by multiple columns, you can put them in order using the chaining above.

Answer 3

    var users = (from i in db.Records
                         where i.Form.CompetitionID == cID
                         group i by new {i.Nickname} into g
                         orderby g.Count() descending, 
                         select new TopUserModel()
    {
        Nickname = g.Key,
        Position = g.Count()
        Date = g.Max(r => r.DateAdded)
    }).Take(100

).OrderBy(c => c.Date).ToList();

Answer 4

Just add max date for nickname to ordering. You also can introduce new range variable for position:

var users = (from r in db.Records
             where r.Form.CompetitionID == cID
             group r by r.Nickname into g
             let position = g.Count()
             orderby position descending, g.Max(r => r.DateAdded)
             select new TopUserModel {
                 Nickname = g.Key,
                 Position = position
             }).Take(100).ToList();

Answer 5

Question is already answered here: OrderBy a date field with linq and return ToList()

Add at the end of your users statement

    .OrderBy(e => e.Date).ToList();