EF Code First 4.1 - 如何使用默认配置一对多关系

Question

我有一个Customer实体,它引用了一组地址.这里的复杂性是我希望能够将特定地址识别为默认地址.

如果可能的话,我想在Customer表中保存默认地址的FK.这似乎比在地址表中有一列来识别默认值更优雅.

在定义这种关系方面,我在使用流畅的API方面遇到了困难.当我运行以下代码时,我得到一个异常,其中说: "保存未公开其关系的外键属性的实体时发生错误.EntityEntries属性将返回null,因为无法将单个实体标识为异常的来源通过在实体类型中公开外键属性,可以更容易地在保存时处理异常.有关详细信息,请参阅InnerException."无法确定依赖操作的有效排序.由于外键约束,模型要求或存储生成的值,可能存在依赖关系."

我创建了一个控制台应用程序来显示确切的问题.在这个测试应用程序中,我有一个Customer实体,一个Address和flient api配置.

任何帮助将非常感激:

using System;
using System.Collections.Generic;
using System.Data.Entity.ModelConfiguration;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;

namespace OneToManyWithDefault
{

    public class Customer
    {
        private ICollection<Address> m_Addresses;

        public Customer()
        {
            Addresses = new List<Address>();
        }

        public int Id { get; set; }
        public string CompanyName { get; set; }
        public virtual ICollection<Address> Addresses
        {
            get
            {
                if (m_Addresses == null)
                {
                    m_Addresses = new List<Address>();
                }
                return m_Addresses;
            }
            set
            {
                m_Addresses = value;
            }
        }
        public Address DefaultAddress { get; set; }
        public int DefaultAddressId { get; set; }

    }

    public class Address
    {
        public int Id { get; set; }
        public string Town { get; set; }
        public Customer Customer { get; set; }
    }

    public class MyContext
        : DbContext
    {
        public DbSet<Customer> Customers { get; set; }

        public MyContext(string connectionString)
            : base(connectionString)
        {

        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new CustomerConfiguration());
            modelBuilder.Configurations.Add(new AddressConfiguration());
            base.OnModelCreating(modelBuilder);
        }
    }

    public class CustomerConfiguration
        : EntityTypeConfiguration<Customer>
    {
        public CustomerConfiguration()
            : base()
        {
            HasKey(p => p.Id);
            Property(p => p.Id)
                .HasColumnName("Id")
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
                .IsRequired();
            Property(p => p.CompanyName)
                .HasColumnName("Name")
                .IsRequired();

            // Configure the mapping for the Default Address (this is likely to be wrong!):
            HasRequired(p => p.DefaultAddress).WithMany()
                .Map(x => x.MapKey("DefaultAddressId"))
                .WillCascadeOnDelete(false);
            HasRequired(p => p.DefaultAddress)
                .WithMany()
                .HasForeignKey(x => x.DefaultAddressId);

            ToTable("Customers");
        }
    }

    public class AddressConfiguration
        : EntityTypeConfiguration<Address>
    {
        public AddressConfiguration()
            : base()
        {
            HasKey(p => p.Id);
            Property(p => p.Id)
                .HasColumnName("Id")
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
                .IsRequired();
            Property(p => p.Town)
                .HasColumnName("Town")
                .IsRequired();

            HasRequired(p => p.Customer)
                .WithMany(c => c.Addresses)
                .Map(x => x.MapKey("CustomerId"));

            ToTable("Addresses");
        }
    }

    class Program
    {
        private const string ConnectionString =
            @"Server=.\sql2005;Database=OneToManyWithDefault;integrated security=SSPI;";

        static void Main(string[] args)
        {
            Customer headOffice = new Customer();
            headOffice.CompanyName = "C1";

            Address address = new Address();
            address.Town = "Colchester";
            headOffice.Addresses.Add(address);

            address = new Address();
            address.Town = "Norwich";
            headOffice.Addresses.Add(address);
            headOffice.DefaultAddress = address;

            MyContext context = new MyContext(ConnectionString);
            context.Customers.Add(headOffice);
            context.SaveChanges();

            Console.WriteLine("Done.");
            Console.ReadLine();
        }
    }
}

非常感谢,

保罗.

Answer 1

我不明白EF在那里谈论的是"异常中没有暴露的外键".我认为内部异常是重要的部分:

无法确定相关操作的有效排序.由于外键约束,模型要求或存储生成的值,可能存在依赖关系.

我认为,在模型中的问题是,你有之间的相互依存Customer和Address:一个地址需要一个客户(你已经将其标记为需要在你的映射代码),并在另一方面客户需要的地址(是默认地址要求由于不可为空的外键和由于您的映射代码而导致的.那么,EF不知道在您的示例代码中首先保存哪个实体 - 默认地址或客户？两个实体都需要使用有效的FK约束来保存另一个实体的主键.

我能看到的最简单的解决方案是在模型中使默认地址可选,然后保存两次(我省略了按惯例工作的映射):

public class Customer
{
    private ICollection<Address> m_Addresses;

    public Customer() { Addresses = new List<Address>(); }

    public int Id { get; set; }
    public string CompanyName { get; set; }
    public virtual ICollection<Address> Addresses { get { ... } set { ... } }
    public Address DefaultAddress { get; set; }
    public int? DefaultAddressId { get; set; } // FK for optional relationship
}

public class Address
{
    public int Id { get; set; }
    public string Town { get; set; }
    public Customer Customer { get; set; }
}

// ...

public class CustomerConfiguration : EntityTypeConfiguration<Customer>
{
    public CustomerConfiguration() : base()
    {
        Property(p => p.CompanyName)
            .HasColumnName("Name")
            .IsRequired();

        HasMany(c => c.Addresses)
            .WithRequired(a => a.Customer)
            .Map(x => x.MapKey("CustomerId"));
    }
}

public class AddressConfiguration : EntityTypeConfiguration<Address>
{
    public AddressConfiguration() : base()
    {
        Property(p => p.Town)
            .HasColumnName("Town")
            .IsRequired();
    }
}

然后你的程序看起来像这样:

static void Main(string[] args)
{
    Customer headOffice = new Customer();
    headOffice.CompanyName = "C1";

    Address address = new Address();
    address.Town = "Colchester";
    headOffice.Addresses.Add(address);

    address = new Address();
    address.Town = "Norwich";
    headOffice.Addresses.Add(address);

    //headOffice.DefaultAddress = address;
    //We don't set the default address here as SaveChanges would throw an
    //exception. But because it is optional now we are allowed to leave it null.

    MyContext context = new MyContext(ConnectionString);
    context.Customers.Add(headOffice);
    context.SaveChanges();

    headOffice.DefaultAddress = address; // headoffice and address have now PKs
    context.SaveChanges(); // Updates headoffice in the DB with default address
}

这双SaveChanges是丑陋的,但我没有看到另一种方式.