c# - Entity Framework 代码优先 - 来自同一张表的两个外键

Question

我刚开始使用 EF 代码，所以我是这个主题的初学者。

我想在 Teams 和 Matches 之间建立关系:

1 场比赛 = 2 支球队(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; }
}

我得到一个异常(exception):

The referential relationship will result in a cyclical reference that is not allowed. [ Constraint name = 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);
    }
}

主键按默认约定映射。团队必须有两场比赛。您不能让两个 FK 引用单个集合。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。