using System.Collections.Generic;

using System.Linq;

using System;

using Microsoft.EntityFrameworkCore;

​

namespace EFTest

{

    public class Blog

    {

        public int BlogId { get; set; }

​

        public string Url { get; set; }

​

        public string Name { get; set; }

        public virtual ICollection<Post> Posts { get; set; }

    }

​

    public class Post

    {

        public int Id { get; set; }

​

        public string Title { get; set; }

​

        public string Content { get; set; }

​

        public virtual ICollection<Blog> Blogs { get; set; }

    }

​

    public class BlogPost

    {

        public Guid OID { get; set; }

        public Blog Blog { get; set; }

​

        public Post Post { get; set; }

    }

​

    public class BloggingContext : DbContext

    {

        public BloggingContext()

        {

        }

​

        public BloggingContext(DbContextOptions<BloggingContext> options) : base(options)

        {

        }

​

        protected override void OnModelCreating(ModelBuilder modelBuilder)

        {

            base.OnModelCreating(modelBuilder);

            // Setting the key here causes entites to not load into collections, even if the key is correctly set later

            modelBuilder.Entity<BlogPost>().HasKey(x=>x.OID);

            modelBuilder.Entity<Blog>().HasMany(x => x.Posts).WithMany(x => x.Blogs)

                .UsingEntity<BlogPost>(

                x => x.HasOne(x => x.Post).WithMany(),

                x => x.HasOne(x => x.Blog).WithMany()

                // Setting the key here works properly, unless it was also set before

                //, x => x.HasKey(x => x.OID)

                );

        }

​

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

​

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

    }

​

    public class BlogService

    {

        private BloggingContext _context;

        public BlogService(BloggingContext context)

        {

            _context = context;

        }

​

        public void Add(string url)

        {

            var blog = new Blog{Url = url};

            blog.Posts = new List<Post>{new Post{Title = "Test"}};

            _context.Blogs.Add(blog);

            _context.SaveChanges();

        }

​

        public IEnumerable<Blog> Find(string term)

        {

            return _context.Blogs.Where(b => b.Url.Contains(term)).OrderBy(b => b.Url).ToList();

        }

    }

​

    class Program

    {

        static void Main(string[] args)

        {

            Console.WriteLine("This is an example of using EF Core InMemory Database");

            Console.WriteLine("======================================================");

            Console.WriteLine("");

            var options = new DbContextOptionsBuilder<BloggingContext>().UseInMemoryDatabase(databaseName: "Add_writes_to_database").Options;

            // Run the test against one instance of the context

            using (var context = new BloggingContext(options))

            {

                var service = new BlogService(context);

                service.Add("http://sample.com");

            }

            // Use a separate instance of the context to verify correct data was saved to database

            using (var context = new BloggingContext(options))

            {

                Console.WriteLine($"In collection Blog.Posts: {context.Blogs.Include(x => x.Posts).First().Posts.Count}");

                Console.WriteLine($"In ChangeTracker Blogs: {context.ChangeTracker.Entries<Blog>().Count()}");

                Console.WriteLine($"In ChangeTracker Posts: {context.ChangeTracker.Entries<Post>().Count()}");

                Console.WriteLine("");

                Console.WriteLine($"In database single Blog: {context.Blogs.Single().BlogId}");

                Console.WriteLine($"In database single Post: {context.Posts.Single().Id}");

                Console.WriteLine($"In database Blog<->Post: {context.Posts.Single(x=>x.Blogs.Contains(context.Blogs.Single()))==context.Posts.Single()}");

                Console.WriteLine("");

                Console.WriteLine($"In ChangeTracker BlogPosts: {context.ChangeTracker.Entries<BlogPost>().Count()}");

                Console.WriteLine($"In collection Blogs..Posts: {context.Blogs.Include(x => x.Posts).SelectMany(x=>x.Posts).Count()}");

            }

        }

    }

}