Linq OrderByDescending，首先为null

Question

I have a field in my database that holds a DateTime?. I would like to sort the results so that the NULLs show up at the top, then descending by DateTime, eg,

null
null
2012-04-01
2012-01-01
2011-09-04

The reason is that I am looking at expiration dates, though some entries do not expire.

Answer 1

您可以从排序表达式返回DateTime.MaxValue而不是null ，因此首先排序具有null日期的行：

yourData.OrderByDescending(row => row.dateTimeField ?? DateTime.MaxValue);

Answer 2

I find the most straightforward approach to be:

data.OrderBy(Function(o) o.myDate IsNot Nothing).ThenByDescending(Function(o) o.myDate)

in C# I think...

data.OrderBy(o => o.myDate != null).ThenByDescending(o => o.myDate)

This will also work with LINQ to SQL. I'm not sure if if(nullable, value) will successfully translate to SQL.

Answer 3

You could try something like this:

var nulls = table.Where(x => x.NullableDateTimeField == null);
var notNulls = table.Where(x => x.NullableDateTimeField != null);

var result = nulls.Concat(notNulls.OrderByDescending(x => x.NullableDateTimeField));

It's more "obviously correct" than "likely to be super-efficient", but it's at least a starting point.

Answer 4

Take a look at David Oesterreich's blog:

var queryResult =
orderedProducts from enumerableProducts
order by orderedProducts.ProductName,
orderedProducts.Price != null ? 1 : 0 descending,
orderedProducts.Price
select orderedProducts;

Answer 5

像上面接受的版本，但具有c＃v6的语法

tickets.OrderByDescending(x => x?.Erstellt ?? DateTime.Now)