我如何将自定义制作的虚拟对象关联到像实体框架一样工作的关系对象？

Question

我有一个customerdetails和customerAddress对象。构造函数如下：

public class CustomerDetails
{
    [Key]
    public int CustomerID { get; set; }

    [Required]
    [StringLength(50)]
    public string CustomerName { get; set; }

    public int AddressID { get; set; }

    public virtual CustomerAddress customerAddress { get; set; }
}

public class CustomerAddress
{
    [Key]
    public int AddressID { get; set; }

    [Required]
    [StringLength(200)]
    public string Address { get; set; }
    public virtual ICollection<CustomerDetails> CustomerDetails { get; set; }
}

我已经从生成的实体框架中复制了这两个构造函数。

填充客户列表和地址列表

List<CustomerDetails> customers = new List<CustomerDetails>();
List<CustomerAddress> addresses = new List<CustomerAddress>();

SqlCommand cmd = new SqlCommand("select * from Customerdetails", con);

using (IDataReader rdr = cmd.ExecuteReader())
{
    while (rdr.Read())
    {
        CustomerDetails customer = new CustomerDetails
                    {
                        CustomerID = Convert.ToInt32(rdr["CustomerID"]),
                        AddressID = Convert.ToInt32(rdr["AddressID"]),
                        CustomerName = rdr["CustomerName"].ToString()
                    };
        customers.Add(customer);
    }
}

cmd = new SqlCommand("select * from CustomerAddress", con);

using (IDataReader rdr = cmd.ExecuteReader())
{
    while (rdr.Read())
    {
        CustomerAddress address = new CustomerAddress
                    {
                        AddressID = Convert.ToInt32(rdr["AddressID"]),
                        Address = rdr["Address"].ToString()
                    };
                    addresses.Add(address);
    }
}

我已经使用sqldatareader在尝试使用linq绑定数据以显示客户地址时

GridView1.DataSource = from c in customers
                       select new { c.CustomerName, c.customerAddress.AddressID};
GridView1.DataBind();

，它不按预期工作。我有一个错误：

对象引用未设置为对象的实例

对象引用未设置为我知道会发生的 。但是，使虚拟对象链接到关系对象以使参考可以工作的诀窍是什么？

Answer 1

我认为您可能需要自己填充虚拟属性，或者只是删除它们并在查询中使用内部连接。

// populate
For Each CustomerDetail from db        
    IF CustomerDetail.AddressId NOT IN addresses
       Fetch CustomerAddress from Db
       addresses.Add(CustomerAddress )
    ELSE
       FETCH CustomerAddress from addresses
    END
    CustomerDetail.customerAddress = CustomerAddress
    CustomerAddress.CustomerDetails.Add(CustomerDetail)
    customers.Add(CustomerDetail)


//inner join
from c in customers
      join a in addresses on c.AddressID equals a.AddressID
      select new { c.CustomerName, a.Address}