EF core RC2 One to One relationship

[amirjalali1]

Steps to reproduce

Following the instruction here at the ef core doc.
and then using command line

dotnet ef migrations add
dotnet ef database update

the created relationship is one to many instead of one to one.

also i have tried to create models like this :

   public class Blog
    {
        public int BlogId { get; set; }
        public string Url { get; set; }
        public int BlogImageId { get; set; }
        public virtual BlogImage BlogImage { get; set; }
    }

    public class BlogImage
    {
        public int BlogImageId { get; set; }
        public byte[] Image { get; set; }
        public string Caption { get; set; }
        public int BlogId { get; set; }
        public virtual Blog Blog { get; set; }
    } 

and the related modelbuilder

  modelBuilder.Entity<Blog>()
                .HasOne(p => p.BlogImage)
                .WithOne(i => i.Blog)
                .HasForeignKey<BlogImage>(b => b.BlogId);

with no success

The issue

One to Many relationship is created instead of one to one

Further technical details

EF Core version: "1.0.0-rc2-final"
Operating system:
Visual Studio version: 2015 update 2 enterprise

Other details about my project setup:

[smitpatel]

Can you also explain what you mean by One to Many relationship is created instead of one to one ?

[ajcvickers]

Confirmed that the index created for the FK is not unique.

[divega]

Same here.

using System;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Xunit;

namespace Repro5623
{
    public class Tests
    {
        [Fact]
        public void One_to_one_relationships_are_one_to_one()
        {
            using (var context = new MyContext())
            {
                context.Database.EnsureDeleted();
                context.Database.EnsureCreated();
            }

            using (var context = new MyContext())
            {
                var blog = new Blog { Url = "http://blogs.msdn.com/diego" };
                var blogImage1 = new BlogImage { Caption = "Image1", Blog = blog };
                context.BlogImages.Add(blogImage1);
                context.SaveChanges();
            }

            using (var context = new MyContext())
            {
                var blog = context.Blogs.First();
                var blogImage2 = new BlogImage { Caption = "Image2", Blog = blog };
                context.BlogImages.Add(blogImage2);
                context.SaveChanges();
            }

            using (var context = new MyContext())
            {
                var images = context.BlogImages.Include(i => i.Blog).ToList();
                Assert.Same(images[1], images[1].Blog.BlogImage);
                Assert.Same(images[0], images[0].Blog.BlogImage); //fails
            }
        }
    }

    public class Blog
    {
        public int BlogId { get; set; }
        public string Url { get; set; }

        public BlogImage BlogImage { get; set; }
    }

    public class BlogImage
    {
        public int BlogImageId { get; set; }
        public byte[] Image { get; set; }
        public string Caption { get; set; }

        public int BlogId { get; set; }
        public Blog Blog { get; set; }
    }

    public class MyContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<BlogImage> BlogImages { get; set; }


        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                .UseSqlServer("Data Source = (localdb)\\mssqllocaldb;Initial Catalog=Repro5623;Integrated Security=yes");
        }
    }
}

[smitpatel]

See #700 (comment)
This was our decision not to make unique index for one-to-one relationship. Our code treats the one-to-one relationship in its way and never add duplicates but we don't enforce that in database.

[ajcvickers]

@smitpatel I'm not sure where on that issue there was a decision to not make the index unique, but I may be missing something, @divega @rowanmiller @bricelam @AndriySvyryd Thoughts?

[bricelam]

+1 It should be a unique index. #2868 was done to support this on SQL Server.