EF Core 中的可空拥有类型

Question

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));

但是当我将我的 DbContext 与 Address as null 提交时，我得到了这个错误：

InvalidOperationException: 'Member' 的实体正在共享表 'Members' 与 'Member.Address#StreetAddress'，但没有实体 具有相同键值 'Id:-2147480644' 的这种类型 标记为“已添加”。

然后我从构造函数中实例化了地址和位置，现在我可以保存实体了。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。

难道不能创建可以为空的 Owned Types 吗？

Answer 1

难道不能创建可以为空的 Owned Types 吗？

从 EF Core 3 开始，这现在是可能的 ?。

所有家属现在都是可选的。 （在预览版 4 中发货）： Source

---

Sample Code:

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
}

Answer 2

Owned Types 的限制之一是不支持可选（即可为空）。 我建议你关注this thread。

在我的解决方案中，我使用空对象方法并使用 IsEmpty 方法来了解地址是否为空，而不是询问地址是否为空。我希望这种方法对您有所帮助。

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

实体框架document 声明

对拥有的实体类型的引用导航不能为空，除非它们 被显式映射到与所有者不同的表中

所以，事实上，您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中，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，拥有的实体变为可为空。

Answer 4

在这里查看：https://msdn.microsoft.com/en-us/magazine/mt846463.aspx 并向下滚动到“允许空值对象的临时解决方法”。

可以在此处找到更短的示例：https://entityframeworkcore.com/knowledge-base/48063630/nullable-owned-types-in-ef-core

如果没有这种解决方法，我会很高兴能够做到这一点，但我认为这还不可能。