使用EF映射现有数据库中的关系

Question

I am using an existing database that I am unfortunately unable to change, and seem to be having trouble creating a relationship. I'm relatively new to EF, and after some searches have found users trying to achieve something similar, however the advice given does not seem to work in this situation.

I have the following classes:

public partial class Order
{
    public int Id { get; set; }
    public int BillingAddressId { get; set; }
    public int ShippingAddressId { get; set; }
    //more values

    public virtual Address ShippingAddress { get; set; }
    public virtual Address BillingAddress { get; set; }
}

public partial class Address
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    //more values
}

I'd like to be able to access the Shipping/Billing addresses through navigational properties within the order. The ShippingAddressId / BillingAddressId fields both relate to Id in Address class but is unfortunately not set up in the database as a foreign key.

I believe the relationship I'm trying to achieve is many-one. ie An Order has one Shipping Address(Address), but an Address can be the Shipping Address of many Orders.

I've tried multiple variations of the following:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{

    modelBuilder.Entity<Order>().HasOptional(o => o.ShippingAddress)
        .WithMany()
        .HasForeignKey(o => o.ShippingAddressId);

}

But every time I try to access Order.ShippingAddress.FirstName, I get a null reference exception.

Is what I'm trying to achieve possible?

Answer 1

If you have disabled lazy loading you will need to 'include' the navigation property in your query

You can do this with one of the following:

context.Orders.Include(o=>o.ShippingAddress).Where..... // make sure you are `using System.Data.Entity;`
context.Orders.Include("ShippingAddress").Where.....

in addition if your relationship is optional you will need to make the FK id nullable eg:

public int? BillingAddressId { get; set; }
public int? ShippingAddressId { get; set; }