Question

从列表中

class Delivery
{
    public string ProductCode
    {
        get;
        set;
    }

    public DateTime? OrderedDate
    {
        get;
        set;
    }

    public DateTime? DeliveryDate
    {
        get;
        set;
    }

    public Delivery(string pcode, DateTime? orddate, DateTime? deldate)
    {
        ProductCode = pcode;
        OrderedDate = orddate;
        DeliveryDate = deldate;
    }
}


List<Delivery> DeliveryList = new List<Delivery>();
DeliveryList.Add(new Delivery("P001",new DateTime(2009,01,27),null));
DeliveryList.Add(new Delivery("P007",new DateTime(2009,05,17),null));
DeliveryList.Add(new Delivery("P031", new DateTime(2008, 03, 15),
new DateTime(2008,04 ,22)));
DeliveryList.Add(new Delivery("P011",new DateTime(2009,01,27),
new DateTime(2009,02,12)));
DeliveryList.Add(new Delivery("P041",new DateTime(2009,01,27),null));
DeliveryList.Add(new Delivery("P051", new DateTime(2009, 01, 27),
new DateTime(2009, 02, 12)));
DeliveryList.Add(new Delivery("P501",new DateTime(2009,01,27),null));
DeliveryList.Add(new Delivery("P801",new DateTime(2009,01,27),null));

var query = DeliveryList.OrderBy(p => p.DeliveryDate);

出于报告目的，在LINQ执行期间，用什么方法替换空值（基于交付日期）消息“尚未交付”（DateTime是值类型）。

Answer 1

var result = DeliveryList.Select(x => new
{
    ProductCode = x.ProductCode,
    OrderedDate = x.OrderedDate,
    DeliveryDate = x.DeliveryDate.HasValue 
        ? x.DeliveryDate.Value.ToString() : "Yet to be delivered"
}).OrderBy(p => p.DeliveryDate).ToArray();

Answer 2

我不是100％肯定你的要求，但听起来你想将DeliverList转换成一个字符串集合，表明它们何时被交付。如果您希望字符串“尚未交付”，则为null DeliveryDate。如果是这样，请尝试以下方法。

var dates = DeliveryList
  .Select(x => x.DeliverDate 
     ? x.DeliverDate.Value.ToString 
     : "Yet to be delivered");

Answer 3

达林的解决方案很整洁，我会继续使用它。作为替代考虑......

如果您希望保持类型与上面的解决方案一样，则会创建一个匿名类型，并且交付日期可能会以字符串形式结束。

List<Delivery> query = (from d in DeliveryList
                        select new Delivery
                        (
                              d.ProductCode, 
                              d.OrderedDate, 
                              d.DeliveryDate ?? DateTime.Now
                        )).OrderBy(p=>p.DeliveryDate).ToList();

如果您的Delivery类中有一个空构造函数，则可以执行类似

的操作

List<Delivery> query2 = (from d in DeliveryList
                         select new Delivery
                         {
                             DeliveryDate = d.DeliveryDate ?? DateTime.Now,
                             OrderedDate = d.OrderedDate,
                             ProductCode = d.ProductCode
                          }).OrderBy(p=>p.DeliveryDate).ToList();

如果它是空的，那么你必须做的一件事就是对你的DeliveryDate进行有意义的替换。我不认为DateTime.Now会有用，现在你会遇到DateTime字段。显而易见的优点是，您正与一个强烈投射的List对象坐在一起。并且有助于我猜你以后是否会将逻辑放入你的构造函数中。

C＃LINQ用有意义的字符串替换空值

3 个答案: