实体框架代码优先-来自同一表的两个外键

我刚开始使用EF代码，因此我是该主题的总入门者。

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循环引用。[约束名称= Match_GuestTeam]

如何使用两个指向同一个表的外键创建这样的模型？

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);
    }
}

默认情况下，主键是映射的。球队必须有两场比赛。您不能有两个FK引用的单个集合。匹配映射没有级联删除，因为它在这些自引用多对多中不起作用。

也可以ForeignKey()在导航属性上指定属性：

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

这样，您无需向该OnModelCreate方法添加任何代码

我知道这是一个已有多年历史的职位，您可以使用上述解决方案解决您的问题。但是，我只想建议仍然需要使用InverseProperty的人。至少您不需要在OnModelCreating中进行任何更改。

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/zh-cn/data/jj591583?f = 255 & MSPPError = -2147217396#Relationships

您也可以尝试以下方法：

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; }
}

当使FK列允许NULL时，您就在打破循环。或者我们只是在欺骗EF模式生成器。

就我而言，这种简单的修改解决了这个问题。

这是因为默认情况下启用了“级联删除”。问题是，当您在实体上调用删除时，它也会删除每个f键引用的实体。您不应该使“必需”的值可为空以解决此问题。更好的选择是删除EF Code First的Cascade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。

InverseProperty EF Core中的解决方案使解决方案变得简单，干净。

逆属性

因此，所需的解决方案是：

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; }
}