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,所以我在这个主题中完全是初学者.

我想在团队和比赛之间建立关系:1场比赛= 2队(主场,客场)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]

如何创建这样的模型,同一个表有2个外键？TIA.

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);
    }
}

主键按默认约定映射.团队必须有两个比赛集合.您不能拥有两个FK引用的单个集合.匹配是在没有级联删除的情况下映射的,因为它在这些自引用多对多中不起作用.

Answer 2

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,你不需要任何代码添加到OnModelCreate方法

Answer 3

我知道这是一个几年的帖子,你可以解决上述解决方案的问题.但是,我只想建议对仍然需要的人使用InverseProperty.至少你不需要在OnModelCreating中改变任何东西.

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 4

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这个问题.

Answer 5

这是因为默认情况下启用Cascade Deletes.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"值可以为空来解决此问题.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,明确指示何时为每个子节点执行级联删除可能更安全.实体.

Answer 6

InverseProperty 在 EF Core 中使解决方案变得简单和干净。

反性质

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; }
}