C# ASP.Net - 尝试从表中删除数据时出错

Question

我有表格 Player 和表格 Statistic 以及在这个问题中不重要的其他表格。 Table Player 有 PK Player_ID，它在 table Statistic 中是 FK。这些表之间的关系是一对多的（一个玩家可以拥有更多的统计数据）。

代码如下： GenericRepository（我已经创建了它以具有独特的 CRUD 方法类）

public async Task<int> Delete<T>(Guid id) where T : class
{
        try
        {
            T entity = await Get<T>(id);
            Context.Set<T>().Remove(entity);
            return await Context.SaveChangesAsync();
        }
        catch (Exception ex)
        {
            throw ex;
        }
}

PlayerRepository（用于管理对 Player 表的操作）

public async Task<int> Delete(Guid id)
{
        try
        {
            var player = await GenRepository.Get<Player>(id);
            if (player == null)
            {
                return 404;
            }
            else
            {
                return await GenRepository.Delete(player);
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
}

PlayerService(WebAPI中repository和controller的连接)

public async Task<int> Delete(Guid id)
{
        try
        {
            return await PlayerRepository.Delete(id);
        }
        catch (Exception ex)
        {
            throw ex;
        }
}

播放器控制器

[HttpDelete]
    [Route("deleteplayer")]
    public async Task<HttpResponseMessage> Delete(Guid id)
    {
        try
        {
            var Finder = Mapper.Map<PlayerView>(await PlayerService.Get(id));
            if(Finder == null)
            {
                return Request.CreateErrorResponse(HttpStatusCode.BadRequest, "Player doesn't exist in database.");
            }

            var Response = await PlayerService.Delete(id);
            var profile = "../../../app/pictures/FootballFanAppPictures/" + Finder.Club_ID.ToString().ToUpper() + "/profiles/" + id.ToString().ToUpper() + ".png";
            var details = "../../../app/pictures/FootballFanAppPictures/" + Finder.Club_ID.ToString().ToUpper() + "/" + id.ToString().ToUpper() + ".png";
            if (System.IO.File.Exists(profile))
            {
                System.IO.File.Delete(profile);
            }
            if (System.IO.File.Exists(details))
            {
                System.IO.File.Delete(details);
            }
            return Request.CreateResponse(HttpStatusCode.OK, Response);
        }
        catch(Exception ex)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex);
        }
    }

实体模型：

-数据库模型

 public partial class Player
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Player()
    {
        this.Statistic = new HashSet<Statistic>();
    }

    public System.Guid Player_ID { get; set; }
    public System.Guid Club_ID { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public double Height { get; set; }
    public int Weight { get; set; }
    public System.DateTime BirthDate { get; set; }
    public string Nationality { get; set; }
    public string Position { get; set; }
    public int Shirtnmbr { get; set; }

    public virtual Club Club { get; set; }
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Statistic> Statistic { get; set; }
}
using System;
using System.Collections.Generic;

public partial class Statistic
{
    public System.Guid Statistic_ID { get; set; }
    public System.Guid Player_ID { get; set; }
    public int Goals { get; set; }
    public int Assists { get; set; }
    public int FoulsFor { get; set; }
    public int FoulsAgainst { get; set; }
    public int ShotsTotal { get; set; }
    public int ShotsGoal { get; set; }

    public virtual Player Player { get; set; }
}

-域模型（在存储库中使用）

public class PlayerDomain : IPlayerDomain
{
    public Guid Player_ID { get; set; }
    public Guid Club_ID { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public double Height { get; set; }
    public int Weight { get; set; }
    public DateTime BirthDate { get; set; }
    public string Nationality { get; set; }
    public string Position { get; set; }
    public int Shirtnmbr { get; set; }
    public virtual ICollection<IStatisticDomain> Statistic { get; set; }
}
public class StatisticDomain: IStatisticDomain
{
    public Guid Statistic_ID { get; set; }
    public Guid Player_ID { get; set; }
    public int Goals { get; set; }
    public int Assists { get; set; }
    public int FoulsFor { get; set; }
    public int FoulsAgainst { get; set; }
    public int ShotsTotal { get; set; }
    public int ShotsGoal { get; set; }
}

-查看模型（用于控制器）

public class PlayerView
{
    public Guid Player_ID { get; set; }
    public Guid Club_ID { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public double Height { get; set; }
    public int Weight { get; set; }
    public DateTime BirthDate { get; set; }
    public string Nationality { get; set; }
    public string Position { get; set; }
    public int Shirtnmbr { get; set; }
    public virtual ICollection<StatisticView> Statistic { get; set; }
}
public class StatisticView
{
    public Guid Statistic_ID { get; set; }
    public Guid Player_ID { get; set; }
    public int Goals { get; set; }
    public int Assists { get; set; }
    public int FoulsFor { get; set; }
    public int FoulsAgainst { get; set; }
    public int ShotsTotal { get; set; }
    public int ShotsGoal { get; set; }
}

每个类都在一个单独的文件中。我使用数据库优先方法，所以我得到了 .edmx 文件和数据库模型。数据库是在 SQL Server Management Studio 中创建的。

我可以更新播放器，但是当我尝试删除它时，我收到了这个错误：

操作失败：无法更改关系，因为一个或多个外键属性不可为空。当对关系进行更改时，相关的外键属性将设置为空值。如果外键不支持空值，则必须定义新关系，必须为外键属性分配另一个非空值，或者必须删除不相关的对象。

我在 google 和 stackoverflow 上搜索了各种答案，但找不到解决我问题的答案

Answer 1

在调用此行之前：

var Response = await PlayerService.Delete(id);

您将需要检索分配给您尝试删除的玩家的统计数据列表。

然后循环遍历每个统计信息并首先从数据库中删除这些统计信息。

var stats = Finder.Statistic.ToList();

if(stats != null && stats.Any())
{
   foreach(var stat in stats)
   { 
      //retrieve your stat record here from the database
      //check that the stat record is not null
      //delete your stat record here
   }
}

那么您应该能够删除您的玩家记录，因为不再有对其的引用。

或

您可以将 ON DELETE CASCADE 设置为 true，但您需要注意完全了解播放器删除时将删除的所有内容。

Answer 2

我没有在您的代码中看到有关 Player delete 的统计信息删除。 在删除玩家之前，您需要先删除所有与玩家相关的统计信息。如果有剩余，播放器将在删除操作中失败。

Answer 3

设置 PrimaryKey 和 Foreignkey 关系：根据@Bad Dub 的建议。