[英]Entity Framework 5.0 composite foreign key to non primary key - is it possible?
我在.net 4.5控制台应用程序中使用Entity Framework 5.0.0.0,并且必须访问其中有两个表且它们之间具有外键关系的数据库,如下所示:
奇怪的是,外键不在B(AId)
到A(AId)
之间B(Almost1, Almost2)
而在B(Almost1, Almost2)
与A(Almost1, Almost2)
A(AId)
。 SQL Server允许这样做,因为Almost1
和Almost2
组合是唯一的,并且都不是可以为null的(至少在表A
上-在B
它们是可选关系,但是通过by)。
这是用于创建这种情况的一些SQL:
CREATE TABLE [dbo].[A](
[AId] [int] IDENTITY(1,1) NOT NULL,
[Almost1] [int] NOT NULL,
[Almost2] [int] NOT NULL,
CONSTRAINT [PK_A] PRIMARY KEY CLUSTERED
(
[AId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
CONSTRAINT [A_Constraint] UNIQUE NONCLUSTERED
(
[Almost1] ASC,
[Almost2] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
CREATE TABLE [dbo].[B](
[BId] [int] IDENTITY(1,1) NOT NULL,
[Almost1] [int] NULL,
[Almost2] [int] NULL,
CONSTRAINT [PK_B] PRIMARY KEY CLUSTERED
(
[BId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
ALTER TABLE [dbo].[B] ADD CONSTRAINT [FK_A_B] FOREIGN KEY([Almost1], [Almost2])
REFERENCES [dbo].[A] ([Almost1], [Almost2])
事实是,Entity Framework似乎不允许这样做-是这种情况还是我只是未正确定义模型?
这是我的C#:
public class MyContext : DbContext
{
public MyContext(string connectionString) : base(connectionString)
{
MyAs = Set<A>();
MyBs = Set<B>();
}
public DbSet<A> MyAs { get; private set; }
public DbSet<B> MyBs { get; private set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
var aEntity = modelBuilder.Entity<A>();
aEntity.ToTable("A");
aEntity.HasKey(a => a.AId);
var bEntity = modelBuilder.Entity<B>();
bEntity.ToTable("B");
bEntity.HasKey(a => a.BId);
bEntity
.HasOptional(b => b.A)
.WithMany(a => a.Bs)
.Map(m => m.MapKey("Almost1", "Almost2"));
}
}
public class A
{
public int AId { get; set; }
public int Almost1 { get; set; }
public int Almost2 { get; set; }
public virtual ICollection<B> Bs { get; private set; }
public void AddB(B b)
{
if (b == null) throw new ArgumentNullException("b");
if (Bs == null) Bs = new List<B>();
if (!Bs.Contains(b)) Bs.Add(b);
b.A = this;
}
}
public class B
{
public int BId { get; set; }
public virtual A A { get; set; }
}
class Program
{
static void Main()
{
using (var ctx = new MyContext(@"connection string"))
{
ctx.MyAs.Add(new A { Almost1 = 1, Almost2 = 1 });
ctx.SaveChanges();
}
}
}
它抛出一个InvalidOperationException
:
指定的关联外键列'Almost1,Almost2'无效。 指定的列数必须与主键列数匹配。
如果我忽略AId
列,而是使Almost1
和Almost2
成为复合主键,那么我的OnModelCreating
方法现在看起来像这样:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
var aEntity = modelBuilder.Entity<A>();
aEntity.ToTable("A");
aEntity.HasKey(a => new { a.Almost1, a.Almost2 });
aEntity.Ignore(a => a.AId);
var bEntity = modelBuilder.Entity<B>();
bEntity.ToTable("B");
bEntity.HasKey(a => a.BId);
bEntity
.HasOptional(b => b.A)
.WithMany(a => a.Bs)
.Map(m => m.MapKey("Almost1", "Almost2"));
}
它可以工作,但是我并不是真的想要这样做,因为还有一个表(我们称它为C
),该表通过使用AId
列以传统方式与A
,并且外键从C.AId
到A.AId
。
是的,我知道这有点奇怪-但是可以在Entity Framework中处理吗?
如前所述,由于EF不支持唯一键和其他SQL对象。 我最终创建了一些脚本作为嵌入式资源,并让它们作为放置/创建初始化程序的种子过程的一部分执行。
不知道这是否允许您在代码中的对象之间导航,但是在一个过程中更新数据库非常好用。
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