实体框架1：1关系FK

Question

I've asked a similar question before, but wanted to post an updated question and include all the necessary code required to illustrate:

I've got 2 entities; Cart and Shopper. They have a 1:1 relationship. There are times when I don't want to have to load up the nav properties to read the FK value. I've created the entities as described below and set the relationship between cart and shopper (see mapping classes below) but EF is not populating the FK properties on the entities (see the unit test below).

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace ClassLibrary1
{
    public class Cart
    {
        public int ID { get; set; }
        public int ShopperID { get; set; }
        public virtual  Shopper Shopper { get; set; }
    }

    public class Shopper
    {
        public int ID { get; set; }
        public int CartID { get; set; }
        public virtual Cart Cart { get; set; }
    }

    public class CartMap:EntityTypeConfiguration<Cart>
    {
        public CartMap()
        {
            this.HasKey(t => t.ID);

            // Properties

            // Table & Column Mappings
            this.ToTable("Cart", "Cart2");
            this.Property(t => t.ID).HasColumnName("ID");
            this.Property(t => t.ShopperID).HasColumnName("ShopperID");
            //this.HasRequired(t => t.Shopper)
            //    .WithRequiredPrincipal(t => t.Cart);
        }

    }

    public class ShopperMap : EntityTypeConfiguration<Shopper>
    {
        public ShopperMap()
        {
            this.HasKey(t => t.ID);

            // Properties

            // Table & Column Mappings
            this.ToTable("Shopper", "Cart2");
            this.Property(t => t.ID).HasColumnName("ID");
            this.Property(t => t.CartID).HasColumnName("CartID");

            //// Relationships
            this.HasRequired(t => t.Cart)
                .WithRequiredDependent(t => t.Shopper)
                .WillCascadeOnDelete(true);
        }
    }

    public class CartDbContext : DbContext
    {
        public IDbSet<Cart> Carts { get; set; }
        public IDbSet<Shopper> Shoppers { get; set; }
        public CartDbContext():base("name=CartTest")
        {

        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Configurations.Add(new CartMap());
            modelBuilder.Configurations.Add(new ShopperMap());
        }
    }

    public class DBSeedingData : DropCreateDatabaseAlways<CartDbContext>
    {
        protected override void Seed(CartDbContext context)
        {
            var cart1 = new Cart{Shopper = new Shopper()};
            var cart2 = new Cart {Shopper = new Shopper()};
            base.Seed(context);
            context.Carts.Add(cart1);
            context.Carts.Add(cart2);
            context.SaveChanges();
        }
    }

    [TestClass]
    public class TestClass
    {
        [ClassInitialize]
        public static void RunOnceForAllTests(TestContext testContext)
        {
            Console.WriteLine("Initializing Database");
            using (var ctx = new CartDbContext())
            {
                try
                {
                    Database.SetInitializer(new DBSeedingData());
                    ctx.Database.Initialize(true);
                    Console.WriteLine("Database Dropped, Created & Seeded.");
                }
                catch (Exception ex)
                {
                    throw ex;
                }
            }
        }
        [TestMethod]
        public void CanReadAllCarts()
        {
            using (var ctx = new CartDbContext())
            {
                foreach (var cart in ctx.Carts)
                {
                    Console.WriteLine(" actual: Cart Id: {0} Shopper Id: {1} Shopper's Cart Id: {2}", cart.ID, cart.ShopperID, cart.Shopper.CartID);
                    Assert.IsTrue(cart.ID > 0, "Cart PK was not set");
                    Assert.IsTrue(cart.ShopperID > 0, "Shopper FK in Cart was not set");
                    Assert.IsNotNull(cart.Shopper, "Failed to load navigation properties");
                    Assert.IsTrue(cart.Shopper.CartID > 0, "Cart FK in Shopper was not set");
                }    
            }    
        }
    }  
}

What am I missing here? I've been stuck trying to solve this problem for a week.

Answer 1

I've experienced this before and also had trouble doing one to one in EF. We did a work around wherein just have one navigation property between the two entities. In your case, pick whether you would put the navigation property in Cart or Shopper class. Basically, this is a mapping in EF where only one side has a nav property. The downside is that the one with no nav property is blind and you can't tell who it's related to. Here's an article about it.

Let's say you put the nav property in the Shopper class

public class Cart
{
    public int ID { get; set; }

    // no nav property for Shopper
}

public class Shopper
{
    public int ID { get; set; }
    public int CartID { get; set; }
    public virtual Cart Cart { get; set; }
}

then you'll map it like so:

public class ShopperMap : EntityTypeConfiguration<Shopper>
{
    public ShopperMap()
    {
        // other mappings

        // mapping to cart, notice that the WithMany() is empty           
        this.HasRequired(t => t.Cart)
            .WithMany()
            .HasForeignKey(t => t.CartID);
    }
}

You'll see in the article that EF Code-First (or EF in general) does not support one-to-one foreign key associations. This work around worked for us so I hope it does for you too.