Question

反正我是否可以停止转换两次？

allObjects.Where(x => 
  Convert.ToDateTime(x.MyDate).DayOfWeek != DayOfWeek.Saturday &&
  Convert.ToDateTime(x.MyDate).DayOfWeek != DayOfWeek.Sunday).ToList()

假设我无法改变＆＃34; MyDate＆＃34;到datetime停止必须首先进行转换

Answer 1

对于这些类型的案例，使用查询理解表格通常更容易。

var q = from obj in allObjects
        let day = Convert.ToDateTime(obj.MyDate).DayOfWeek
        where day != DayOfWeek.Saturday
        where day != DayOfWeek.Sunday
        select obj;
var result = q.ToList();

请注意，Tim Schmelter给出的答案是该查询的流畅形式;我发现理解形式更容易阅读和推理。

Answer 2

假设我无法将“MyDate”的类型更改为停止的日期时间必须首先进行转换

你为什么这么认为？那将是最好的选择

如果您不能这样做，您可以将结果存储为匿名类型：

var objectList = allObjects
   .Select(x => new { Object = x, Date = Convert.ToDateTime(x.MyDate) })
   .Where(x => x.Date.DayOfWeek != DayOfWeek.Saturday && x.Date.DayOfWeek != DayOfWeek.Sunday)
   .Select(x => x.Object)
   .ToList();

Answer 3

制作帮助扩展方法将使您的查询更具可读性：

static class DayOfWeekExtensions {
    public static bool IsWeekEnd(DayOfWeek dow) {
        return dow == DayOfWeek.Saturday || dow == DayOfWeek.Sunday;
    }
}

现在您的查询可以按如下方式重写：

var notOnWeekEnds = allObjects
    .Where(x => !Convert.ToDateTime(x.MyDate).DayOfWeek.IsWeekEnd())
    .ToList()

Answer 4

你可以这样做：

allObject.Where(x => { var dt = Convert.ToDateTime(x.MyDate);
                       return dt.DayOfWeek != DayOfWeek.Saturday && dt.DayOfWeek != DayOfWeek.Sunday;
                     }).ToList();

Answer 5

是 -

allObjects.Where(x => {
     var dateConvered = Convert.ToDateTime(x.MyDate);
     return dateConvered .DayOfWeek != DayOfWeek.Saturday && dateConvered.DayOfWeek != DayOfWeek.Sunday; }).ToList();

Answer 6

我可能会走这条路。我讨厌多个OR逻辑。

var allObjects = new List<Foo>
{
    new Foo { MyDate = "3/10/18" },
    new Foo { MyDate = "3/11/18" },
    new Foo { MyDate = "3/12/18" },
    new Foo { MyDate = "3/13/18" },
    new Foo { MyDate = "3/14/18" }
};
var valuesToRemove = new DayOfWeek[]
{ 
    DayOfWeek.Saturday, DayOfWeek.Sunday 
};
var list = allObjects.Where   //<-- This is the part that will interest you
( 
    x => Array.IndexOf
    (
        valuesToRemove, 
        Convert.ToDateTime(x.MyDate).DayOfWeek
    ) == -1
);
Console.WriteLine(string.Join("\r\n", list));

输出：

3/12/18
3/13/18
3/14/18

Code on DotNetFiddle

Answer 7

这对于在LINQ表达式中重用计算值可能没有帮助，但在您的特定情况下，您可以将其重写为：

var weekendDays = new [] { DayOfWeek.Saturday, DayOfWeek.Sunday };

var weekdayObjects = allObjects.Where(x =>
    !weekendDays.Contains(Convert.ToDateTime(x.MyDate).DayOfWeek)
).ToList();

当你需要做一个Convert.To时，Linq声明？

7 个答案: