Entity Framework not inserting a related record in a 1:0..1 relationship (Unexpected result)

Question

it's been a while since my last post, this time i need some help to understand something that is goin on with Entity Framework (SQL Server) in c# using Code-First aproach.

Let me show you the code i have:

Blog.cs

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Helper.Models
{
    public class Blog
    {
        [Key]
        public int BlogId { get; set; }
        public string BlogTitle { get; set; }
        public virtual ICollection<Post> Posts { get; set; }
        public virtual Author Author { get; set; }
    }
}

Author.cs

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace Helper.Models
{
    public class Author
    {
        [Key,ForeignKey("Blog")]
        public int AuthorId { get; set; }
        public string Name { get; set; }
        public string Address { get; set; }
        public virtual Blog Blog { get; set; }
    }
}

RegularAuthor.cs

using System;

namespace Helper.Models
{
    public class RegularAuthor : Author
    {
        public DateTime DateOfFirstBlogPost { get; set; }
    }
}

GuestAuthor.cs

namespace Helper.Models
{
    public class GuestAuthor : Author
    {
        public string OriginalBlogAccess { get; set; }
    }
}

DefaultDB.cs

using Helper.Models;
using System.Data.Entity;

    namespace EF_Basics
    {
        public class DefaultDB : DbContext
        {
            public DefaultDB(): base("EFDemo")
            {

            }
            public DbSet<Blog> Blogs { get; set; }
            public DbSet<Post> Posts { get; set; }
            public DbSet<Category> Categories { get; set; }
            public DbSet<Author> Authors { get; set; }
        }
    }

Program.cs

using Helper.Models;
using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace EF_Basics
{
    class Testing
    {
        static void Main(string[] args)
        {
            TestInsert2();
            Console.WriteLine("Press any key to exit...");
            Console.ReadLine();
        }

        private static void TestInsert2()
        {
            using (DefaultDB ctx = new DefaultDB())
            {
                RegularAuthor author1 = new RegularAuthor()
                {
                    Name = "First Author",
                    Address = GetLocalIpAddress(),
                    DateOfFirstBlogPost = DateTime.Now
                };

                GuestAuthor guest1 = new GuestAuthor()
                {
                    Name = "Second Author",
                    Address = GetLocalIpAddress(),
                    OriginalBlogAccess = "Never"
                };

                List<Blog> BlogList = new List<Blog>()
                {
                    new Blog
                    {
                        Author = author1,
                        BlogTitle = "Mid Century Modern DIY Dog House Build"
                    },
                    new Blog
                    {
                        Author = guest1,
                        BlogTitle = "Elf Doughnut Box Printable"
                    },
                    new Blog
                    {
                        Author = author1,
                        BlogTitle = "5 Ways to Make Giant Candy for a Candyland Theme"
                    }
                };

                foreach (var blog in BlogList)
                {
                    Console.WriteLine($"Adding '{blog.BlogTitle}' by '{blog.Author.Name}'");
                    ctx.Blogs.Add(blog);
                    Thread.Sleep(1000);
                    Console.WriteLine();
                }

                ctx.SaveChanges();
            }
        }

        private static string GetLocalIpAddress()
        {
            var host = Dns.GetHostEntry(Dns.GetHostName());
            foreach (var ip in host.AddressList)
            {
                if (ip.AddressFamily == AddressFamily.InterNetwork)
                {
                    return ip.ToString();
                }
            }
            throw new Exception("No network adapters with an IPv4 address in the system!");
        }
    }
}

So... now that we have all the pertinent code, when i run it all get "most" of the info into the database, but the last record just ignores all of the author data. I also included a snapshot of the SQL and the result after running the code.

Answer 1

I think the problem is that you are adding the blog to the database. Instead you should add the authors with their list of blogs.

The author class should have a list of blogs, so when you add an Author entity you can add as many Blogs as you require.

public List<Blog> Blogs { get; set; }

In the Blog class you can change the following:

public Author Author { get; set; }

This is an example of what should be done:

    private static void TestInsert2()
    {
     using (DefaultDB ctx = new DefaultDB())
     {
       RegularAuthor author1 = new RegularAuthor()
       {
         Name = "First Author",
         Address = GetLocalIpAddress(),
         DateOfFirstBlogPost = DateTime.Now
       };
       GuestAuthor guest1 = new GuestAuthor()
       {
        Name = "Second Author",
        Address = GetLocalIpAddress(),
        OriginalBlogAccess = "Never"
       };

    author1.Blogs = new List<Blog>
    {
       new Blog        
       {
         Author = author1,
         BlogTitle = "Mid Century Modern DIY Dog House Build"
       },
        new Blog
       {
         Author = author1,
         BlogTitle = "5 Ways to Make Giant Candy for a Candyland Theme"
       }
    }

    guest1.Blogs = new List<Blog>
    {
       new Blog
       {
         Author = guest1,
         BlogTitle = "Elf Doughnut Box Printable"
       }
    }
    context.Add(author1);
    context.Add(guest1);
    ctx.SaveChanges();
    }
   }

As the blogs are referenced by the Blog property in the author object they will be added to the database

Edit:

This has taken some effort, but I think I have the solution. The table relationship is not correct.

What you are trying to do is to have an author with many blogs. Now that implies that the author object must have a collection of blogs.

The relationship you must have is the following:

In this scenario Blog has a foreign key to Author and as suggested in my main answer the Author class must have a collection of Blogs:

public partial class Author
{  
    public Author()
    {
        Blogs = new HashSet<Blog>();
    }
    public int authorId { get; set; }
    public string name { get; set; }
    public virtual ICollection<Blog> Blogs { get; set; }
}

Meanwhile the Blog class:

public partial class Blog
{
    public int blogId { get; set; }
    public string blogTitle { get; set; }
    public int? authorId { get; set; }
    public virtual Author Author { get; set; }
}

Your model will be:

   public Model1()
    {
    }

    public virtual DbSet<Author> Authors { get; set; }
    public virtual DbSet<Blog> Blogs { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Author>()
            .Property(e => e.name)
            .IsUnicode(false);

        modelBuilder.Entity<Blog>()
            .Property(e => e.blogTitle)
            .IsUnicode(false);
    }

Before running the code:

After running the code: