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[英]How to create a table with two foreign keys pointing to the same table using Entity Framework Code First
[英]Entity Framework Code First - two Foreign Keys from same table
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 Teams 和 Matches 之间创建关系:
1 场比赛 = 2 支球队(主队、客队)和结果。
我认为创建这样一个模型很容易,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 ]
我怎样才能创建这样一个模型,同一个表有 2 个外键?
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。
也可以在navigation属性上指定ForeignKey()
属性:
[ForeignKey("HomeTeamID")]
public virtual Team HomeTeam { get; set; }
[ForeignKey("GuestTeamID")]
public virtual Team GuestTeam { get; set; }
这样您就不需要向OnModelCreate
方法添加任何代码
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
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。
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。
EF Core中的InverseProperty
使解决方案变得简单而干净。
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; }
}
我知道这是一个很老的问题,但在 2021 年来到这里,下面的 EF Core > 3 解决方案对我有用。
确保外键可以为空
指定删除时的默认行为
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); }
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