using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using Microsoft.EntityFrameworkCore;

namespace NoTrackingBug
{
    public class BloggingContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<Post> Posts { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlite("Data Source=blogging.db");
        }
    }

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

        public List<Post> Posts { get; set; }

        public int OwnerId { get; set; }
        public Person Owner { get; set; }
    }

    public class Post
    {
        public int PostId { get; set; }
        public string Title { get; set; }

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

    public class Person
    {
        public int PersonId { get; set; }
        public string Name { get; set; }

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

    class Program
    {
        static void Main(string[] args)
        {
            // Setup the example
            using (var db = new BloggingContext())
            {
                if (!db.Blogs.Any())
                {
                    db.Blogs.Add(new Blog
                    {
                        Url = "http://blogs.msdn.com/adonet",
                        Posts = new List<Post>{
                            new Post { Title = "SomeTitle" }
                        },
                        Owner = new Person
                        {
                            Name = "Kobert"
                        }
                    });

                    db.SaveChanges();
                }
            }

            // Explicit load and .NoTracking => does not work for References
            using (var db = new BloggingContext())
            {
                db.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;

                var blog = db.Blogs
                    .AsTracking()
                    .Single();

                db.Entry(blog)
                    .Collection(b => b.Posts)
                    .Load();

                db.Entry(blog)
                    .Reference(b => b.Owner)
                    .Load();

                Debug.Assert(blog.Posts != null);
                Debug.Assert(blog.Owner != null); // <== This will fail!
            }

            // Eager load and .NoTracking => does work
            using (var db = new BloggingContext())
            {
                db.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;

                var blog = db.Blogs
                    .Include(b => b.Posts)
                    .Include(b => b.Owner)
                    .AsTracking()
                    .Single();

                Debug.Assert (blog.Posts != null);
                Debug.Assert (blog.Owner != null);
            }
            
            // Explicit load and .TrackAll => does work
            using (var db = new BloggingContext())
            {
                var blog = db.Blogs
                    .Single();

                db.Entry(blog)
                    .Collection(b => b.Posts)
                    .Load();

                db.Entry(blog)
                    .Reference(b => b.Owner)
                    .Load();

                Debug.Assert(blog.Posts != null);
                Debug.Assert(blog.Owner != null);
            }
        }
    }
}