c# - 我该如何解决无法隐式将 Generic.List< > 转换为 Generic.List< >

Question

如何修复无法隐式转换 System.Collections.Generic.List <RPHistory>至System.Collections.Generic.List <RPHistory>异常错误。

我正在尝试将两个实体组合在一起以获得单个列表

RP实体类:

 public class RP 
        {
            public int ID { get; set; }
            public int RPID { get; set; }
            public string Name { get; set; }
            public int ProductID { get; set; }
        }

RPHistory 实体类:

public class RPHistory: 
    {
        public int ID { get; set; }
        public int RPID { get; set; }
        public string Name { get; set; }
        public int ProductID { get; set; }
    }

我创建了第三个类

RpWithHistory 类:

public class RpWithHistory {
  public int ID;
  public int RPID;
  public string Name;
  public int ProductID;

  public List<RPHistory> History;
}

Linq 查询

var RPs = await Context.RP.Where(b => b.ProductID  == request.ID)
                              .Select(x=> new RpWithHistory {
                                               ID = x.ID, 
                                               RPID = x.RPID, 
                                               Name = x.Name, 
                                               ProductID = x.ProductID, 
                                               History = Context.RPHistory
                                                                .Where(y=> y.RPID 
                                                                        == x.RPID)
                                                                .ToList()
                                               }
                                      ).ToListAsync();

但我收到此错误，

>Cannot implicitly convert System.Collections.Generic.List <RPHistory> to
>System.Collections.Generic.List <RPHistory> exception error

谢谢!

Answer 1

我不知道你为什么要这么做。我可以建议这个吗？

您不需要一路走来创建一个将两者结合起来的类。只需在 RP 上创建一个指向 RPHistory 对象的导航属性即可。

public class RP 
{
    public int ID { get; set; }
    public int RPID { get; set; }
    public string Name { get; set; }
    public int ProductID { get; set; }
    public ICollection<RPHistory> HistoryList { get; set; } // Navigation Property
}

public class RPHistory: 
{
    public int ID { get; set; }
    public int RPID { get; set; }
    public string Name { get; set; }
    public int ProductID { get; set; }

    [ForeignKey(nameof(RPID))] // Identify the Foreign Key from RP Class
    public RP RP { get; set; } // Navigation back to RP
}

然后您可以使用 LINQ 将所有内容链接到一个列表中:

var RPs = Context.RP.Where(rp => rp.ProductID  == request.ID)
                 .Include(rp=>rp.RPHistory) // This includes RPHistory
                 .ToList();