如何在C#中将子类型转换为父对象 [英] how to typecast Child to Parent object in C#

问题描述

我有一个 ASP.Net Core 2.1 C#应用程序.

这就是我的DTO的样子.

This is how my DTOs looks like.

public class Movie
{
  public int Id { get; set;}

  public bool IsSpecial {get; set;}

  public IEnumerable<Ticket> Tickets{ get; set;}
}

机票(基本舱位)

 public class Ticket
 {
   public int Id { get; set;}

   public string Name { get; set;}

   public decimal price { get; set;}
 } 

特价机票(儿童/派生类)

TicketsSpecial (Child/Derived Class)

 public class TicketsSpecial : Ticket
 {
    public string SpecialProp1 { get; set;}

    public string SpecialProp2 { get; set;}

 }

WebAPI控制器

public class MovieController : ControllerBase
{

  public IActionResult Post([FromBody]Movie movie)
  {
      if(movie.IsSpecial)
      {
         var tickets = movie.Tickets;
         movie.Tickets = new List<TicketsSpecial>(); 
        movie.Tickets = tickets;
         SomeMethod(movie.Tickets);// throws run time error
         movie.Tickets = tickets;
      }
  }

  private bool SomeMethod(IEnumerable<TicketSpecial> tickets)
  {
  }
}

RTE

无法转换类型的对象'System.Collections.Generic.List 1 [Ticket]'键入'System.Collections.Generic.List 1 [TicketSpecial]'

Unable to cast object of type 'System.Collections.Generic.List1[Ticket]' to type 'System.Collections.Generic.List1[TicketSpecial]'

此外，TicketSpecial的额外属性不可用，因为它不在Ticket类中.

Also,the extra properties of TicketSpecial is unavailable as it's not present in Ticket class.

所以我反之亦然

public class Movie
{
  public int Id { get; set;}

  public IEnumerable<TicketSpecial> Tickets{ get; set;}
}

这样，我得到了额外字段的值，即.门票特殊道具.但是再次进行类型转换时会引发错误.

Going this way, I get the values of extra fields ie. TicketSpecial props. But again while typecasting it throws the error.

public IActionResult Post([FromBody]Move movie)
  {
      if(!movie.IsSpecial)
      {
         var tickets = movie.Tickets;
         movie.Tickets = new List<Ticket>();//throws Compile time error 

      }
  }

但是这引发了错误，因为CS0266无法将类型'System.Collections.Generic.List'隐式转换为'System.Collections.Generic.IEnumerable'.存在显式转换(您是否缺少演员表?)

But this throws the error as CS0266 Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)

我想使用#2(第二种方式)解决此问题，因为在 move.IsSpecial 为true

如何处理这种类型转换?谢谢！

How to handle this typecasting? Thanks!

推荐答案

必须准备电影中的特殊票的清单.这些票并传递给消费者

Must prepare a list of special tickets from movie.Tickets and pass to the consumer

var specialTickets = new List<TicketsSpecial>();
specialTickets.AddRange(movie.Tickets.OfType<TicketsSpecial>());
SomeMethod(specialTickets);

在您的示例中，第二个分配将Tickets属性分配回原始属性，原始属性是票证列表，而不是特殊票证.

In your example, the second assignment assigned the tickets property back to the original one which is a list of ticket, not special ticket.

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