using System;

using System.Collections.Generic;

using System.Threading;

using Microsoft.EntityFrameworkCore;

​

public class Program

{

    public static void Main()

    {

        using var ctx = new MyDbContext();

        var customer = new Customer(Industry.IndustryMedia);

        ctx.Customers.Attach(customer);

        Console.WriteLine("Main thread count of Industry.IndustryMedia.Customers: {0}", Industry.IndustryMedia.Customers.Count);

        // Other threads can observe the new customer before it saved to the data persistence layer

        ThreadPool.QueueUserWorkItem(state =>

        {

            Console.WriteLine("Thread {0} count of Industry.IndustryMedia.Customers: {1}", Thread.CurrentThread.ManagedThreadId, Industry.IndustryMedia.Customers.Count);

        });

        // (lazy way to make sure the other thread has finished)

        Thread.Sleep(1000);

        Console.WriteLine("Only now calling saving changes");

        ctx.SaveChanges();

    }

​

    public class MyDbContext : DbContext

    {

        public DbSet<Customer> Customers => Set<Customer>();

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

        {

            optionsBuilder.UseInMemoryDatabase("MyDb");

        }

    }

​

    public class Customer

    {

        public long Id { get; private set; }

​

        public Industry Industry { get; private set; }

​

        protected Customer()

        {

        // parameterless constructor supports EF

        }

​

        public Customer(Industry industry)

        {

            Industry = industry;

        }

    }

​

    public class Industry

    {

        public long Id { get; private set; }

​

        public string Name { get; }

​

        public static readonly Industry IndustryMedia = new("Media");

        protected Industry()

        {

        // parameterless constructor supports EF

        }

​

        private Industry(string name)

        {

            Name = name;

        }

​

        public virtual ICollection<Customer> Customers { get; private set; } = new List<Customer>();

    }

}