Exception has occurred: CLR/System.AggregateException An unhandled exception of type 'System.AggregateException' occurred in Microsoft.Extensions.D

Question

Hi im working of a text book called: Microservices in dotnet book second edition, and have reached a part in chapter where the author talks about Dependency Injection (DI) using a package called Scrutor. However, examples of the book are done in .Net 5 (netcoreapp3.0) and I've been working with .Net 6 which does not have a StartUp file but rather has a Program File as the main file, when a project is generated.

so in the author's code for DI there is the following in StartUp.cs

...
public void ConfigureServices(IServiceCollection services)
{
  services.AddControllers();
  services.Scan(selector =>
  selector
        .FromAssembly<StartUp>()
        .AddClasses()
        .AsImplementedInterfaces());
}
...

And my .net 6 code is as follows in my Program.cs file

...
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.Scan(scan =>
    scan.FromAssemblyOf<Program>()
    .AddClasses()
    .AsImplementedInterfaces());
...

With my controller code implementation:

namespace ShoppingCartMicroservice.ShoppingCart
{
    using Microsoft.AspNetCore.Mvc;
    [ApiController]
    [Route("/shoppingcart")]
    public class ShoppingCartController : ControllerBase
    {
        private readonly IShoppingCartStore shoppingCartStore;

        public ShoppingCartController(IShoppingCartStore shoppingCartStore)
        {
            this.shoppingCartStore = shoppingCartStore;
        }

        [HttpGet("{userId:int}")]
        public ShoppingCart Get(int userId) =>
            this.shoppingCartStore.Get(userId);

    }
}

The interface:

using ShoppingCartMicroservice.ShoppingCart;

public interface IShoppingCartStore
{
    ShoppingCart Get(int userId);
    void save(ShoppingCart shoppingCart);
}

My In memory Shopping car store:

using ShoppingCartMicroservice.ShoppingCart;

public class ShoppingCartStore : IShoppingCartStore
{
    private static readonly Dictionary<int, ShoppingCart> Database = new Dictionary<int, ShoppingCart>();
    public ShoppingCart Get(int userId) =>
    Database.ContainsKey(userId) ? Database[userId] : new ShoppingCart(userId);

    public void save(ShoppingCart shoppingCart) => 
    Database[shoppingCart.UserId] = shoppingCart;
}

And my logic

namespace ShoppingCartMicroservice.ShoppingCart
{
    using System.Collections.Generic;
    using System.Linq;

    public class ShoppingCart
    {
        private readonly HashSet<ShoppingCartItem> items = new();
        public int UserId { get; }
        public IEnumerable<ShoppingCartItem> Items => this.items;
        public ShoppingCart(int UserId) => this.UserId = UserId;

        public void AddItems(IEnumerable<ShoppingCartItem> shoppingCartItems)
        {
            foreach (var item in shoppingCartItems)
            {
                this.items.Add(item);
            }
        }

        public void RemoveItems(int[] productCatalogueIds) =>
            this.items.RemoveWhere(i => productCatalogueIds.Contains(i.ProductCatalogueId));


    }

    public record ShoppingCartItem
    (
    int ProductCatalogueId,
    string ProductName,
    string Description,
    Money Price
    )
    {
        public virtual bool Equals(ShoppingCartItem? obj) =>
        obj != null && this.ProductCatalogueId.Equals(obj.ProductCatalogueId);

        public override int GetHashCode() =>
        this.ProductCatalogueId.GetHashCode();
    }

    public record Money(string Currency, decimal Amount);
}

However with my implementation, at run time I get the following error:

Exception has occurred: CLR/System.AggregateException
An unhandled exception of type 'System.AggregateException' occurred in Microsoft.Extensions.DependencyInjection.dll: 'Some services are not able to be constructed'
 Inner exceptions found, see $exception in variables window for more details.
 Innermost exception     System.InvalidOperationException : Unable to resolve service for type 'System.Int32' while attempting to activate 'ShoppingCartMicroservice.ShoppingCart.ShoppingCartItem'.
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)

Link to project: https://github.com/dot-net-microservices-in-action/chapter-02