EF Core中的可空拥有类型

Question

我的情况下，我想存储一个地址，但它必须是可选的。

我的映射如下所示：

map.OwnsOne(x => x.Address, cb => cb.OwnsOne(l => l.Location));

但是当将我的DbContext的地址设置为空iam时出现此错误：

InvalidOperationException：'Member'的实体正在与'Member.Address＃StreetAddress'共享表'Members'，但是没有具有相同键值'Id：-2147480644'的此类型的实体被标记为'Added '。

然后，我从构造函数实例化了Address和Location，现在可以保存实体。但是，当再次获取数据时，我也得到了一个实例化的地址，我真的想要一个空值。

不能创建可为空的拥有类型吗？

Answer 1

实体框架文档指出

对拥有的实体类型的引用导航不能为 null，除非它们显式映射到与所有者不同的单独表

所以，事实上，你的问题有一个解决方案。您需要将您拥有的实体映射到单独的表，而不是将其与所有者放在同一个表中。

map.OwnsOne(x => x.Address, cb => cb.OwnsOne(l => l.Location, l=> l.ToTable("Locations")));

通过将位置实体映射到名为Locations的单独表中，拥有的实体可以为空。

Answer 2

拥有类型的限制之一是不支持可选（即可为空）。我建议你关注这个线程。

在我的解决方案中，我使用 Empty Object 方法并使用 IsEmpty 方法来了解地址是否为空，而不是询问地址是否为空。我希望这种方法可以帮助你。

public sealed class Address : ValueObject<Address>
{
    public string StreetAddress1 { get; private set; }
    public string StreetAddress2 { get; private set; }
    public string City { get; private set; }
    public string State { get; private set; }
    public string ZipCode { get; private set; }
    public string Country { get; private set; }

    private Address() { }
    public Address(string streetAddress1, string city, string state, string zipcode, string country)
    {
        StreetAddress1 = streetAddress1;
        City = city;
        State = state;
        ZipCode = zipcode;
        Country = country;
    }

    public Address(string streetAddress1, string streetAddress2, string city, string state, string zipcode, string country)
        : this(streetAddress1, city, state, zipcode, country)
    {
        StreetAddress2 = streetAddress2;
    }

    public static Address Empty()
    {
        return new Address("", "", "", "", "");
    }

    public bool IsEmpty()
    {
        if (string.IsNullOrEmpty(StreetAddress1)
         && string.IsNullOrEmpty(City)
         && string.IsNullOrEmpty(State)
         && string.IsNullOrEmpty(ZipCode)
         && string.IsNullOrEmpty(Country))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

}
public class Firm : AggregateRoot<Guid>
{
    public string Name { get; private set; }
    public Address Address { get; private set; }

    private Firm() { }
    public Firm(string name)
    {
        if (String.IsNullOrEmpty(name))
            throw new ArgumentException();

        Id = Guid.NewGuid();
        Name = name;
        Address = Address.Empty();
    }
}

Answer 3

不能创建可为空的拥有类型吗？

从EF Core 3开始，这已经成为可能。

现在所有依赖项都是可选的。（在预览版4中发货）： 来源

样例代码：

static void Main(string[] args)
{
  using (var context = new OwnedEntityContext())
  {
    context.Add(new DetailedOrder
    {
      Status = OrderStatus.Pending,
      OrderDetails = new OrderDetails
      {
        ShippingAddress = new StreetAddress
        {
          City = "London",
          Street = "221 B Baker St"
        }
        //testing 3.0: "Yes, all dependents are now optional"
        //reference: https://github.com/aspnet/EntityFrameworkCore/issues/9005#issuecomment-477741082
        //NULL Owned Type Testing
        //BillingAddress = new StreetAddress
        //{
        //    City = "New York",
        //    Street = "11 Wall Street"
        //}
      }
    });
    context.SaveChanges();
  }
  //read test
  using (var context = new OwnedEntityContext())
  {
    #region DetailedOrderQuery
    var order = context.DetailedOrders.First(o => o.Status == OrderStatus.Pending);
    Console.Write("NULL Owned Type Test, Is Billing Address NULL?");
    //PRINTS FALSE
    Console.WriteLine($"{order.OrderDetails.BillingAddress == null}");
    #endregion
  }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    #region OwnsOneNested
    modelBuilder.Entity<DetailedOrder>().OwnsOne(p => p.OrderDetails, od =>
    {
        od.OwnsOne(c => c.BillingAddress);
        od.OwnsOne(c => c.ShippingAddress);
    });
    #endregion

    #region OwnsOneTable
    modelBuilder.Entity<DetailedOrder>().OwnsOne(p => p.OrderDetails, od =>
    {
        od.OwnsOne(c => c.BillingAddress);
        od.OwnsOne(c => c.ShippingAddress);
        od.ToTable("OrderDetails");
        //Exception message:Microsoft.Data.SqlClient.SqlException:
        //'Cascading foreign key 'FK_OrderDetails_DetailedOrders_OrderId' cannot
        //be created where the referencing column 'OrderDetails.OrderId' is an identity column.
        //Could not create constraint or index. See previous errors.'
        //3.0 bug: https://github.com/aspnet/EntityFrameworkCore/issues/17448#issuecomment-525444101 
        //fixed in 3.1: https://github.com/aspnet/EntityFrameworkCore/pull/17458
        od.Property("OrderId")
            .ValueGeneratedNever();
    });
    #endregion
}