Question

如何先按null排序布尔值，然后依次为true和false

return View("Index", db.HolidayRequestForms.ToList().OrderByDescending(e => e.Approved).ThenBy(e => e.RequestID))

我正在为布尔使用自定义显示模板，我不知道这是否重要

Answer 1

您可以使用自定义比较器

public class ApprovedComparer : IComparer<bool?>
{
    public int Compare(bool? x, bool? y)
    {
        var a = 0;
        var b = 0;

        if (x.HasValue)
            a = x.Value ? 1 : 2;
        if (y.HasValue)
            b = y.Value ? 1 : 2;

        return a - b;
    }
}

用法：

return View("Index", db.HolidayRequestForms.ToList()
    .OrderBy(e => e.Approved, new ApprovedComparer())
    .ThenBy(e => e.RequestID))

可以在LinqPad（或普通的控制台应用程序）中进行测试

public class Thing
{
    public string Name { get; set; }
    public bool? Approved { get; set; }
}

public class ApprovedComparer : IComparer<bool?>
{
    public int Compare(bool? x, bool? y)
    {
        var a = 0;
        var b = 0;

        if (x.HasValue)
            a = x.Value ? 1 : 2;
        if (y.HasValue)
            b = y.Value ? 1 : 2;

        return a - b;
    }
}

void Main()
{
    var thing1 = new Thing { Approved = null, Name = "Thing 1" };
    var thing2 = new Thing { Approved = true, Name = "Thing 2", };
    var thing3 = new Thing { Approved = false, Name = "Thing 3" };

    //note the 'incorrect' order
    var listOfThings = new[] { thing3, thing2, thing1 };

    listOfThings
        .OrderBy(x => x.Approved, new ApprovedComparer())
        .Select(x => x.Name) //just for outputting the names
        .Dump(); //LinqPad specifc
}

输出

从.net 4.5开始，您可以使用Comparer<T>.Create()创建一个静态比较器，该比较器可以是“内联”的-即，不需要单独的类。

就个人而言，我发现单独的类更易于阅读。不过，只是我的意见。

var comparer = Comparer<bool?>.Create((x, y) =>
   {
       var a = 0;
       var b = 0;

       if (x.HasValue)
           a = x.Value ? 1 : 2;
       if (y.HasValue)
           b = y.Value ? 1 : 2;

       return a - b;
   });

listOfThings
    .OrderBy(x => x.Approved, comparer)
    .Select(x => x.Name) //just for outputting the names
    .Dump(); //LinqPad specifc

Answer 2

您可以使用此：

myList.OrderBy(v => !v)

ASP.NET Order bool未设置

2 个答案: