SO Question 6466936

Example.cs

using System;
using System.Collections.Generic;
using System.Data.Entity;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            CreateData();
            GetData();
        }

        private static void GetData()
        {
            var context = new TestContext();
            var theIssue = context.Issues.Find(1);

            Console.WriteLine("Issue Id {0}", theIssue.ID);
            Console.WriteLine("- Category {0}", theIssue.category.desc);
            Console.WriteLine("- SubCategory {0}", theIssue.subCategory.desc);

        }

        private static void CreateData()
        {
            Console.WriteLine("Creating Data");

            var context = new TestContext();
            var parent = new Category()
            {
                desc = "Parent",

            };
            context.Categories.Add(parent);
            context.SaveChanges();

            var sub = new Category()
            {
                desc = "Sub",
                parentId = parent.ID,
                parentCategory = parent
            };
            context.Categories.Add(sub);
            context.SaveChanges();

            var issue = new Issue()
            {
                category = parent,
                categoryID = parent.ID,
                subCategory = sub,
                subCategoryID = sub.ID,
            };

            context.Issues.Add(issue);
            context.SaveChanges();
            
            Console.WriteLine("Data Created");            
        }
    }


    public class Category
    {
        public int ID { get; set; }
        public string desc { get; set; }
        public int? parentId { get; set; }
        public virtual Category parentCategory { get; set; }

        public virtual ICollection<Issue> issues { get; set; } 
    }

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

        public int categoryID { get; set; }
        public int subCategoryID { get; set; }

        public virtual Category category { get; set; }
        public virtual Category subCategory { get; set; }
    }


    public class TestContext : DbContext
    {
        public DbSet<Category> Categories { get; set; }
        public DbSet<Issue> Issues { get; set; } 

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Category>().HasOptional(c => c.parentCategory).WithMany().HasForeignKey(s => s.parentId);
            modelBuilder.Entity<Issue>().HasRequired(i => i.category).WithMany().HasForeignKey(c => c.categoryID).WillCascadeOnDelete(false);
        }
    }
}