Order.cs

[ApiExplorerSettings(IgnoreApi = true)]
[Authorize] // Controllers that mainly require Authorization still use Controller/View; other pages use Pages
[Route("[controller]/[action]")]
public class OrderController : Controller
{
    private readonly IMediator _mediator;

    public OrderController(IMediator mediator)
    {
        _mediator = mediator;
    }

    [HttpGet]
    public async Task<IActionResult> MyOrders()
    {   
        Guard.Against.Null(User?.Identity?.Name, nameof(User.Identity.Name));
        var viewModel = await _mediator.Send(new GetMyOrders(User.Identity.Name));

        return View(viewModel);
    }
}

{
    private readonly IReadRepository<Order> _orderRepository;

    public GetMyOrdersHandler(IReadRepository<Order> orderRepository)
    {
        _orderRepository = orderRepository;
    }

    public async Task<IEnumerable<OrderViewModel>> Handle(GetMyOrders request,
        CancellationToken cancellationToken)
    {
        var specification = new CustomerOrdersSpecification(request.UserName);
        var orders = await _orderRepository.ListAsync(specification, cancellationToken);

        return orders.Select(o => new OrderViewModel
        {
            OrderDate = o.OrderDate,
            OrderNumber = o.Id,
            ShippingAddress = o.ShipToAddress,
            Total = o.Total()
        });
    }
}

public class CustomerOrdersSpecification : Specification<Order>
{
    public CustomerOrdersSpecification(string buyerId)
    {
        Query.Where(o => o.BuyerId == buyerId)
            .Include(o => o.OrderItems);
    }
}