我有一个引用地址集合的客户实体。 这里的复杂之处在于我希望能够将特定地址标识为默认地址。
如果可能的话,我想在客户表中保存默认地址的 FK。 这似乎比在地址表中使用一列来标识默认值更优雅。
在定义这种关系方面,我在流畅的 API 方面遇到了困难。 当我运行以下代码时,我得到一个异常,上面写着:"保存未公开其关系的外键属性的实体时出错。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,可以更轻松地在保存时处理异常。有关详细信息,请参阅内部异常。"无法确定从属操作的有效顺序。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。 在此测试应用程序中,我有一个客户实体、一个地址和 flient api 配置。
任何帮助将不胜感激:
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。
我不明白 EF 在异常中谈论"未公开的外键"是什么。我认为内部异常是重要的部分:
无法确定有效的订单 对于依赖操作。依赖 可能由于外键而存在 约束、模型要求或 存储生成的值。
我认为您的模型中的问题在于您在Customer
和Address
之间具有相互依赖关系:地址需要一个客户(您已在映射代码中将其标记为必需),另一方面,客户需要一个地址(由于不可为空的外键和由于您的映射代码,默认地址是必需的)。因此,EF 不知道在示例代码中首先保存哪个实体 - 默认地址还是客户?两个实体都需要使用有效的 FK 约束保存另一个实体的主键。
能看到的最简单的解决方案是在您的模型中使默认地址可选,然后保存两次(无论如何,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();
}
}
然后你的程序将如下所示:
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
}
这种双重SaveChanges
很丑陋,但我看不到其他方法。