LinqToDB-EF Core integration

Program.cs

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using LinqToDB;
using LinqToDB.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;

namespace ConsoleApp1
{
    class Program
    {
        class Category
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public ISet<CategoryItem> Items { get; set; }
        }

        class CategoryItem
        {
            public int CategoryId { get; set; }
            public Category Category { get; set; }

            public int ItemId { get; set; }
            public Item Item { get; set; }
        }

        class Item
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public ISet<CategoryItem> Categories { get; set; }
        }

        class DataContext : DbContext
        {
            public DataContext(DbContextOptions options) : base(options)
            {
            }

            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                base.OnModelCreating(modelBuilder);

                modelBuilder.Entity<CategoryItem>()
                    .HasKey(entity => new { entity.CategoryId, entity.ItemId });
            }

            public DbSet<Category> Categories { get; set; }
            public DbSet<CategoryItem> CategoryItems { get; set; }
            public DbSet<Item> Items { get; set; }

            public override void Dispose()
            {
                base.Dispose();
                Debug.WriteLine("Disposed");
            }
        }

        static async Task Main(string[] args)
        {
            LinqToDBForEFTools.Initialize();
            LinqToDB.Data.DataConnection.TurnTraceSwitchOn();
            LinqToDB.Data.DataConnection.WriteTraceLine = (message, displayName) => Debug.WriteLine($"{message} {displayName}");


            var services = new ServiceCollection();

            var optionsBuilder = new DbContextOptionsBuilder<DataContext>()
                .UseSqlServer("Server=localhost;Database=Test;Integrated Security=SSPI;MultipleActiveResultSets=True", o => o.UseRowNumberForPaging());

            services.AddSingleton(optionsBuilder.Options);

            services.AddDbContext<DataContext>();

            using (var sp = services.BuildServiceProvider())
            {
                using (var scope = sp.CreateScope())
                {
                    var ctx = scope.ServiceProvider.GetRequiredService<DataContext>();

                    await ctx.Database.EnsureCreatedAsync();

                    var item1 = new Item
                    {
                        Name = "ItemA",
                    };

                    var item2 = new Item
                    {
                        Name = "ItemB",
                    };

                    var category1 = new Category
                    {
                        Name = "Cat1",
                        Items = new HashSet<CategoryItem>
                        {
                            new CategoryItem { Item = item1 },
                            new CategoryItem { Item = item2 }
                        }
                    };

                    var category2 = new Category
                    {
                        Name = "Cat2",
                        Items = new HashSet<CategoryItem>
                        {
                            new CategoryItem { Item = item2 }
                        }
                    };

                    await ctx.AddRangeAsync(category1, category2);

                    await ctx.SaveChangesAsync();
                }


                using (var scope = sp.CreateScope())
                {
                    var ctx = scope.ServiceProvider.GetRequiredService<DataContext>();

                    var q =
                        from cat in ctx.Categories
                        from catItem in ctx.CategoryItems.LeftJoin(ci => ci.CategoryId == cat.Id)
                        select new { catItem.Item.Name };

                    var r = await q.ToArrayAsyncLinqToDB();
                }
            }
        }
    }
}