State persistence - URL

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace persistence_examples.Controllers
{
    public class Receipt
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public decimal Total { get; set; }
        public List<ReceiptItem> Items { get; set; }
    }

    public class ReceiptItem
    {
        public int ItemNo { get; set; }
        public string ProductName { get; set; }
        public int Quantity { get; set; }
        public decimal Price { get; set; }
        public decimal Value { get; set; }
    }

    [Route("api/[controller]")]
    [ApiController]
    public class ReceiptController : ControllerBase
    {
        private static List<Receipt> _receipts = new List<Receipt>();

        public ReceiptController()
        {
            // If there are no receipts, generate some for testing
            if (!_receipts.Any())
            {
                var totals = new decimal[] { 10.99M, 11.99M, 29.99M, 99.99M };
                var titles = new string[] { "Monthly Subscription", "Monthly Subscription - Family", "Quarterly Subscription", "Annual Subscription" };
                var currentId = 1;
                var rnd = new Random();
                for (var i = 0; i < 100; i++)
                {
                    var rndIdx = rnd.Next(totals.Length);
                    _receipts.Add(new Receipt
                    {
                        Id = currentId,
                        Total = totals[rndIdx],
                        Title = titles[rndIdx],
                    });
                    currentId++;
                }
            }
        }

        [HttpGet()]
        public ActionResult<Receipt> GetAll()
        {
            return Ok(_receipts);
        }


        [HttpGet("{id}")]
        public ActionResult<Receipt> Get(int id)
        {
            var retVal = _receipts.FirstOrDefault(x => x.Id == id);
            if(retVal == null)
                return NotFound();

            return Ok(retVal);
        }

        [HttpGet("[action]")]
        public ActionResult<Receipt> Paged(int page, int size, string orderBy, string direction)
        {
            IEnumerable<Receipt> ordered;

            // Ordering
            if (string.Compare(orderBy, "id", true) == 0)
            {
                ordered = _receipts.OrderBy(x => x.Id);
            }
            else if (string.Compare(orderBy, "title", true) == 0)
            {
                ordered = _receipts.OrderBy(x => x.Title);
            }
            else if (string.Compare(orderBy, "total", true) == 0)
            {
                ordered = _receipts.OrderBy(x => x.Total);
            }
            else
            {
                // default: order by Id
                ordered = _receipts.OrderBy(x => x.Id);
            }

            // For descending order we just reverse it
            if (string.Compare(direction, "desc", true) == 0)
            {
                ordered = ordered.Reverse();
            }


            // Now we can page the correctly ordered items
            var retVal = ordered.Skip(page * size).Take(size);

            return Ok(retVal);
        }

        [HttpGet("[action]")]
        public ActionResult<Receipt> Filtered(string filter)
        {
            var retVal =
                _receipts.Where(x =>
                    x.Title.Contains(filter, StringComparison.InvariantCultureIgnoreCase));

            return Ok(retVal);
        }
    }
}