c# - Entity Framework 5.0b2 代码优先 : One-To-Many and One-To-One for the same table, 带级联删除

Question

经过几个小时的反复试验，我找到了这个 thread其中解释了如何建立具有相同两种类型的一对多关系和一对一关系。

但是，我无法让它与级联删除一起使用:

Thrown: "Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values." (System.Data.UpdateException) Exception Message = "Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values.", Exception Type = "System.Data.UpdateException"

只有在我不取消 1:1 关系(见下面的代码)时才会发生这种情况，我认为这是有道理的，因为它会创建一个无效的引用。我只是想知道是否有更好的方法来表示这一点。

示例代码:

class Program
{
    static void Main(string[] args)
    {
        Database.SetInitializer(new DropCreateDatabaseAlways<Context>());

        using (var ctx = new Context())
        {
            var user = new User();

            ctx.Users.Add(user);
            ctx.SaveChanges();

            var source = new PaymentSource();
            user.PaymentSources = new Collection<PaymentSource>();
            user.PaymentSources.Add(source);
            user.DefaultPaymentSource = source;
            ctx.SaveChanges();

            // if I don't do this, I get ordering exception
            user.DefaultPaymentSource = null;
            ctx.SaveChanges();

            ctx.Users.Remove(user);
            ctx.SaveChanges();

            Assert.Equal(0, ctx.Users.Count());
            Assert.Equal(0, ctx.PaymentSources.Count());
        }
    }
}

public class User
{
    public int Id { get; set; }

    public virtual ICollection<PaymentSource> PaymentSources { get; set; }
    public virtual PaymentSource DefaultPaymentSource { get; set; }
    public int? DefaultPaymentSourceId { get; set; }
}

public class PaymentSource
{
    public int Id { get; set; }
    public virtual User User { get; set; }
    public int UserId { get; set; }
}

public class Context : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<PaymentSource> PaymentSources { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<User>()
            .HasOptional(u => u.DefaultPaymentSource)
            .WithMany()
            .HasForeignKey(u => u.DefaultPaymentSourceId)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<PaymentSource>()
            .HasRequired(p => p.User)
            .WithMany(p => p.PaymentSources)
            .HasForeignKey(p => p.UserId)
            .WillCascadeOnDelete();
    }
}

Answer 1

我列出了其他选项来描述您的抽象:

A.

如何使用 3 个这样的表:

user 1-* paymentSource
user 1-0..1 DefaultPaymentSource
DefaultPaymentSource 0..1-1 PaymentSource

或者这个:

B.

user 1-* paymentSource
user 1-0..1 DefaultPaymentSource
DefaultPaymentSource --derive from--> PaymentSource

或者这个:

C.

user 1-* paymentSource
PaymentSource has addtional boolean field for "IsDefault"

我投票选 B 为最佳。

我敢肯定，从同一个源表到同一个目标表的两个关系不是一个好主意。它可能会破坏有关数据库最佳实践的一些规则或模式。