using System;

using System.Collections.Generic;

using System.Linq;

using Microsoft.EntityFrameworkCore;

using NUnit.Framework;

​

public class Program

{

    public class TestContext : DbContext

    {

        protected override void OnConfiguring(DbContextOptionsBuilder options)

            => options.UseInMemoryDatabase(databaseName: "TestDb");

        protected override void OnModelCreating(ModelBuilder modelBuilder){

            modelBuilder.Entity<LineItem>()

                .HasOne(li => li.OriginLineItemContainer1)

                .WithMany(li => li.NextContainer2LineItems)

                .HasForeignKey(li => li.OriginLineItemContainer1Id);

            modelBuilder.Entity<LineItem>()

                .HasOne(li => li.OriginLineItemContainer2)

                .WithMany(li => li.NextContainer3LineItems)

                .HasForeignKey(li => li.OriginLineItemContainer2Id);

            modelBuilder.Entity<BaseContainer>()

                .HasDiscriminator(bc => bc.Discriminator)

                .HasValue<Container1>("Container1")

                .HasValue<Container2>("Container2")

                .HasValue<Container3>("Container3");

            modelBuilder.Entity<BaseContainer>()

                .HasMany(bc => bc.LineItems)

                .WithOne(); 

        }

    }

    public abstract class BaseContainer

    {

        public int Id {get; set;}

        public List<LineItem> LineItems = new();

        public string Discriminator {get; set;}

    }

​

    public class Container1 : BaseContainer

    {

        public Container1(){

            Discriminator = "Container1";   

        }

    }

    public class Container2 : BaseContainer

    {

        public Container2(){

            Discriminator = "Container2";   

        }

    }

    public class Container3 : BaseContainer

    {

        public Container3(){

            Discriminator = "Container3";   

        }

    }

    public class LineItem

    {

        public int Id {get; set;}

        public LineItem OriginLineItemContainer1 {get;set;}

        public int? OriginLineItemContainer1Id {get; set;}

        public List<LineItem> NextContainer2LineItems {get; set;} = new();

        public LineItem OriginLineItemContainer2 {get; set;}

        public int? OriginLineItemContainer2Id {get; set;}

        public List<LineItem> NextContainer3LineItems {get; set;} = new();

    }

    public static void Main()

    {

        var setupContext = new TestContext();

        var container1 = new Container1();

        var container1LineItem = new LineItem();

        var container2 = new Container2();

        var container2LineItem = new LineItem();

        container2LineItem.OriginLineItemContainer1 = container1LineItem;

        var container3 = new Container3();

        var container3LineItem = new LineItem();

        container3LineItem.OriginLineItemContainer2 = container2LineItem;

        container3LineItem.OriginLineItemContainer1 = container1LineItem;

        container1.LineItems.Add(container1LineItem);

        container2.LineItems.Add(container2LineItem);

        container3.LineItems.Add(container3LineItem);

        setupContext.Add(container1);

        setupContext.Add(container2);

        setupContext.Add(container3);

        setupContext.SaveChanges();

        setupContext.Dispose();

        var validationContext = new TestContext();

        var validationContainer1 = validationContext.Set<Container1>().Include(c => c.LineItems).Single();

        var validationContainer2 = validationContext.Set<Container2>().Include(c => c.LineItems).Single();

        var validationContainer3 = validationContext.Set<Container3>().Include(c => c.LineItems).Single();

        Assert.That(validationContainer1.LineItems[0].NextContainer2LineItems.Count, Is.EqualTo(1));

        Assert.That(validationContainer2.LineItems[0].NextContainer3LineItems.Count, Is.EqualTo(1));

​

    }

}