Entity Framework Code First一对一约束冲突

Question

考虑以下简化模型：

public class Account
{
    public Account()
    {
        Id = Guid.NewGuid();
        ContactCard = new ContactCard();
    }

    //[ForeignKey("ContactCard")]
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Number { get; set; }
    public ContactCard ContactCard { get; set; }
}

public class ContactCard
{
    public ContactCard()
    {
        Id = Guid.NewGuid();
    }

    public Guid Id { get; set; }
    public Account Account { get; set; }
}

public class MightDbContext: DbContext
{
    public DbSet<Account> Accounts { get; set; }
    public DbSet<ContactCard> ContactCards { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Account>().HasRequired(x => x.ContactCard).WithOptional(x => x.Account);
    }
}

public class MightDbInitializer : DropCreateDatabaseIfModelChanges<MightDbContext>
{
    protected override void Seed(MightDbContext context)
    {
        var accounts = new List<Account> 
        {
            new Account()
            {
                Name = "Acme Corporation Pty. Ltd.",
                Number = "001ABC"
            },

            new Account()
            {
                Name = "Three Little Pigs Pty. Ltd.",
                Number = "002DEF"
            }
        };

        accounts.ForEach(c => context.Accounts.Add(c));
    }
}

以下是一个简单的控制台程序，用于迭代 Accounts 和 ContactCards 集合的内容：

static void Main(string[] args)
    {
        Database.SetInitializer<MightDbContext>(new MightDbInitializer());

        using (var context = new MightDbContext())
        {
            foreach (Account c in context.Accounts)
            {
                Console.WriteLine(c.ContactCard.Id);
            }

            var contactCards = context.ContactCards.ToList();  /* ERROR OCCURS HERE */

            foreach (ContactCard a in contactCards)
            {
                Console.WriteLine(a.Id);
            }
        }

        Console.Read();
    }

当我尝试访问ContactCards集合时，为什么会立即出现以下错误：

"Multiplicity constraint violated. The role 'Account_ContactCard_Source' of the relationship 'InvestAdmin.Might.DataAccess.Account_ContactCard' has multiplicity 1 or 0..1."

当我查看实际存储在数据库表中的数据时，所有内容似乎都是正确的。事实上，这里就是那些数据：

Accounts:
Id  Name    Number
ab711bad-1b32-42ca-b68b-12f7be831bd8    Acme Corporation Pty. Ltd.  001ABC
dc20a1dd-0ed4-461d-bc9c-04a85b555740    Three Little Pigs Pty. Ltd. 002DEF

ContactCards:
Id
dc20a1dd-0ed4-461d-bc9c-04a85b555740
ab711bad-1b32-42ca-b68b-12f7be831bd8

为了完整起见，这是在数据库中定义的Account_ContactCard外键约束：

-- Script Date: 06/12/2011 7:00 AM  - Generated by ExportSqlCe version 3.5.1.7
   ALTER TABLE [Accounts] ADD CONSTRAINT [Account_ContactCard] FOREIGN KEY ([Id]) REFERENCES [ContactCards]([Id]) ON DELETE NO ACTION ON UPDATE NO ACTION;

我一直在阅读关于Code First中定义一对一关系的所有内容，尝试了许多不同的配置。但最终都遇到了同样的问题。

- daveywc

Answer 1

我发现，将相关联的ContactCard的创建从Account构造函数中移动到DBInitializer的Seed方法中实际创建Account对象时，可以解决这个问题。因此，看起来这不是（直接）与一对一关系有关的问题。

- daveywc

---

这指引我朝着正确的方向前进。我在构造函数中实例化了一个导航属性。我以为这会被 E.F 覆盖，但显然不是这样。一旦我移除了它，我就不再收到错误消息了。谢谢。 - John Mc

@John Mc，从构造函数中删除属性对我来说是救命稻草。 - D S