实体框架代码优先 - 来自同一个表的两个外键

Question

我刚开始使用 EF 代码，所以我完全是这个主题的初学者。

我想在团队和比赛之间建立关系：

1 场比赛 = 2 支球队（主队、客队）和结果。

我认为创建这样的模型很容易，所以我开始编码：

public class Team
{
    [Key]
    public int TeamId { get; set;} 
    public string Name { get; set; }

    public virtual ICollection<Match> Matches { get; set; }
}


public class Match
{
    [Key]
    public int MatchId { get; set; }

    [ForeignKey("HomeTeam"), Column(Order = 0)]
    public int HomeTeamId { get; set; }
    [ForeignKey("GuestTeam"), Column(Order = 1)]
    public int GuestTeamId { get; set; }

    public float HomePoints { get; set; }
    public float GuestPoints { get; set; }
    public DateTime Date { get; set; }

    public virtual Team HomeTeam { get; set; }
    public virtual Team GuestTeam { get; set; }
}

我得到一个例外：

引用关系将导致不允许的循环引用。 [约束名称 = Match_GuestTeam]

如何创建这样一个模型，同一个表有 2 个外键？

Answer 1

试试这个：

public class Team
{
    public int TeamId { get; set;} 
    public string Name { get; set; }

    public virtual ICollection<Match> HomeMatches { get; set; }
    public virtual ICollection<Match> AwayMatches { get; set; }
}

public class Match
{
    public int MatchId { get; set; }

    public int HomeTeamId { get; set; }
    public int GuestTeamId { get; set; }

    public float HomePoints { get; set; }
    public float GuestPoints { get; set; }
    public DateTime Date { get; set; }

    public virtual Team HomeTeam { get; set; }
    public virtual Team GuestTeam { get; set; }
}


public class Context : DbContext
{
    ...

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Match>()
                    .HasRequired(m => m.HomeTeam)
                    .WithMany(t => t.HomeMatches)
                    .HasForeignKey(m => m.HomeTeamId)
                    .WillCascadeOnDelete(false);

        modelBuilder.Entity<Match>()
                    .HasRequired(m => m.GuestTeam)
                    .WithMany(t => t.AwayMatches)
                    .HasForeignKey(m => m.GuestTeamId)
                    .WillCascadeOnDelete(false);
    }
}

默认约定映射主键。球队必须有两个比赛集合。您不能有两个 FK 引用的单个集合。匹配在没有级联删除的情况下映射，因为它在这些自引用多对多中不起作用。

Answer 2

你也可以试试这个：

public class Match
{
    [Key]
    public int MatchId { get; set; }

    [ForeignKey("HomeTeam"), Column(Order = 0)]
    public int? HomeTeamId { get; set; }
    [ForeignKey("GuestTeam"), Column(Order = 1)]
    public int? GuestTeamId { get; set; }

    public float HomePoints { get; set; }
    public float GuestPoints { get; set; }
    public DateTime Date { get; set; }

    public virtual Team HomeTeam { get; set; }
    public virtual Team GuestTeam { get; set; }
}

当您使 FK 列允许 NULLS 时，您正在打破循环。或者我们只是在欺骗 EF 模式生成器。

就我而言，这个简单的修改解决了问题。

Answer 3

还可以在导航属性上指定ForeignKey() 属性：

[ForeignKey("HomeTeamID")]
public virtual Team HomeTeam { get; set; }
[ForeignKey("GuestTeamID")]
public virtual Team GuestTeam { get; set; }

这样您就不需要在OnModelCreate 方法中添加任何代码

Answer 4

这是因为级联删除默认启用。问题是当您在实体上调用 delete 时，它​​也会删除每个 f-key 引用的实体。您不应将“必需”值设为可空来解决此问题。更好的选择是删除 EF Code First 的级联删除约定：

modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>(); 

在映射/配置时明确指示何时对每个子级执行级联删除可能更安全。实体。

Answer 5

我知道这是一个几年前的帖子，您可以通过上述解决方案解决您的问题。但是，我只是想建议仍然需要的人使用 InverseProperty。至少您不需要更改 OnModelCreating 中的任何内容。

以下代码未经测试。

public class Team
{
    [Key]
    public int TeamId { get; set;} 
    public string Name { get; set; }

    [InverseProperty("HomeTeam")]
    public virtual ICollection<Match> HomeMatches { get; set; }

    [InverseProperty("GuestTeam")]
    public virtual ICollection<Match> GuestMatches { get; set; }
}


public class Match
{
    [Key]
    public int MatchId { get; set; }

    public float HomePoints { get; set; }
    public float GuestPoints { get; set; }
    public DateTime Date { get; set; }

    public virtual Team HomeTeam { get; set; }
    public virtual Team GuestTeam { get; set; }
}

您可以在 MSDN 上阅读有关 InverseProperty 的更多信息：https://msdn.microsoft.com/en-us/data/jj591583?f=255&MSPPError=-2147217396#Relationships

Answer 6

EF Core 中的InverseProperty 使解决方案变得简单而干净。

InverseProperty

所以理想的解决方案是：

public class Team
{
    [Key]
    public int TeamId { get; set;} 
    public string Name { get; set; }

    [InverseProperty(nameof(Match.HomeTeam))]
    public ICollection<Match> HomeMatches{ get; set; }

    [InverseProperty(nameof(Match.GuestTeam))]
    public ICollection<Match> AwayMatches{ get; set; }
}


public class Match
{
    [Key]
    public int MatchId { get; set; }

    [ForeignKey(nameof(HomeTeam)), Column(Order = 0)]
    public int HomeTeamId { get; set; }
    [ForeignKey(nameof(GuestTeam)), Column(Order = 1)]
    public int GuestTeamId { get; set; }

    public float HomePoints { get; set; }
    public float GuestPoints { get; set; }
    public DateTime Date { get; set; }

    public Team HomeTeam { get; set; }
    public Team GuestTeam { get; set; }
}

Answer 7

我知道这是一个很老的问题，但 2021 年来到这里，下面的 EF Core > 3 解决方案对我有用。

1. 确保外键可以为空

2. 指定删除的默认行为

   public class Match 
   { 
      public int? HomeTeamId { get; set; }
      public int? GuestTeamId { get; set; }
   
      public float HomePoints { get; set; }
      public float GuestPoints { get; set; }
      public DateTime Date { get; set; }
   
      public Team HomeTeam { get; set; }
      public Team GuestTeam { get; set; }
   }
   
   protected override void OnModelCreating(ModelBuilder modelBuilder)
   {
       modelBuilder.Entity<Match>()
                   .HasRequired(m => m.HomeTeam)
                   .WithMany(t => t.HomeMatches)
                   .HasForeignKey(m => m.HomeTeamId)
                   .OnDelete(DeleteBehavior.ClientSetNull);
   
       modelBuilder.Entity<Match>()
                   .HasRequired(m => m.GuestTeam)
                   .WithMany(t => t.AwayMatches)
                   .HasForeignKey(m => m.GuestTeamId)
                   .OnDelete(DeleteBehavior.ClientSetNull);
   }