c# - 有没有更好的方法来设置 linq 中项目列表共有的属性

Question

我有以下课程：

public class Vehicle
{
    public string Make { get; set; }
    public DateTime DateManufactured { get; set; }
}

然后我列出了车辆清单，例如：

        var dateTime1 = DateTime.Now.AddDays(-7);
        var dateTime2 = DateTime.Now.AddDays(-8);
        var dateTime3 = DateTime.Now.AddDays(-9);

        var vehicles = new List<Vehicle>
            {
                new Vehicle {Make = "Ferrari", DateManufactured = dateTime1},
                new Vehicle {Make = "Mazda", DateManufactured = dateTime2},
                new Vehicle {Make = "Dodge", DateManufactured = dateTime3},
                new Vehicle {Make = "Holden", DateManufactured = dateTime1},
                new Vehicle {Make = "Chrysler", DateManufactured = dateTime2},
                new Vehicle {Make = "Mazda", DateManufactured = dateTime3},
            };

接下来，我试图获取 DatesManufactured 列表以及每个日期在该日期制造的车辆。

所以我去了：

var vehiclesGroupedByDate = vechicles.GroupBy(x => x.DateManufactured)
                .Select(x => new
                    {
                        x.First().DateManufactured,
                        Vehicles = x.ToList()
                    });

这很好用，但我不确定这x.First()部分。它有效，但感觉不太对劲。有人知道更优雅的编码方式吗？

Answer 1

当您使用GroupBy时，它会创建一个IGrouping<TKey, TItem>，因此您可以简单地执行以下操作：

var vehiclesGroupedByDate = vechicles.GroupBy(x => x.DateManufactured)
            .Select(x => new
                {
                    x.Key,
                    Vehicles = x.ToList()
                });

Answer 2

我看不出您的代码有任何问题，但您也可以使用不需要创建另一个 IEnumerable 的x.Key替代方法。x.First().DateManufactured

Answer 3

GroupBy 公开一个 Key 属性：

var vehiclesGroupedByDate = vechicles.GroupBy(x => x.DateManufactured)
    .Select(x => new
    {
        x.Key,
        Vehicles = x.ToList()
    });