Entity Framework 5.0b2代码优先:同一表的一对多和一对一,带有级联删除 [英] Entity Framework 5.0b2 Code First: One-To-Many and One-To-One for the same table, WITH Cascade Delete
问题描述
经过数小时的反复试验,我到达了线程,其中介绍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。
After several hours of trial and error, I reached to this thread which explains how to establish a One-To-Many relationship and a One-To-One relationship with the same two types.
但是,我无法将其与级联删除一起使用:
However, I cannot get this to work with Cascade Delete:
抛出:无法确定相关
操作的有效顺序。由于外键约束,
模型要求或商店生成的值,因此可能存在依赖关系。
(System.Data.UpdateException)异常消息=无法确定
a依赖操作的有效顺序。由于
是由于外键约束,模型要求或存储生成的$ b,因此可能存在依赖关系$ b values。,异常类型= System.Data.UpdateException
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"
仅当我未取消设置1时才会发生:1关系(请参见下面的代码),考虑到它将创建无效的引用,我认为这是有意义的。我只是想知道是否有更好的方法来表示这一点。
This only happens if I don't unset the 1:1 relationship (see code below), which I guess makes sense given that it would create an invalid reference. I'm just wondering if there is a better way to represent this.
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();
}
}
推荐答案
I列出了描述您的抽象的其他选项:
I listed other options to describe your abstraction:
A。
如何使用像这样的3个表:
How about using 3 tables like that:
user 1-* paymentSource
user 1-0..1 DefaultPaymentSource
DefaultPaymentSource 0..1-1 PaymentSource
或此:
B。
user 1-* paymentSource
user 1-0..1 DefaultPaymentSource
DefaultPaymentSource --derive from--> PaymentSource
或以下方式:
C。
user 1-* paymentSource
PaymentSource has addtional boolean field for "IsDefault"
我对选项B投票是最好的。
I vote for choice B as best one.
我敢肯定,从同一个源表到同一个目标表有两个关系并不是一个好主意。它可能打破了有关数据库最佳实践的某些规则或模式。
I am certain that having two relations comming from the same source table to the same destination table is not going to be a good idea.. it is probably breaking some rule or pattern regarding databases best practice.
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