ASP.NET CORE MVC Loading table page takes too long - asp.net-mvc

Question

I have a table with orders(around 8000 records),
The table takes a few seconds to load.
The reason for that is because one of the field shown on the page is being retrieved from another table
(returnProductName).
when removing this function the table loads fast.
When loading the records I'm using Skip and Take but when retrieving the product name i'm iterating all the Orders since if the user wants to search by product name it will show all results with this product.
The product table is not big (around 70 records)
I can't figure out why the function will make the page load so slow.
I know i can just add the product name column to the table and populate it when ever adding new orders,
but this doesn't sounds right,
Can anyone tell me the reason for this delay?
returnProductName Function :
public string returnProductName(int productId)
{
return (_unitOfWork.Product.GetAll().Where(q => q.Id == productId).Select(q =>
q.ProductName)).FirstOrDefault();
}
Function that loads the page data:
[HttpPost]
public ActionResult GetList()
{
//Server Side parameters
int start = Convert.ToInt32(Request.Form["start"].FirstOrDefault());
int length = Convert.ToInt32(Request.Form["length"].FirstOrDefault());
string searchValue = Request.Form["search[value]"].FirstOrDefault();
string sortColumnName = Request.Form["columns["+Request.Form["order[0][column]"]+"][name]"].FirstOrDefault();
string sortDirection = Request.Form["order[0][dir]"].FirstOrDefault();
List<Order> orderList = new List<Order>();
orderList = _unitOfWork.Order.GetAll().ToList();//Working Fast
int totalRows = orderList.Count;
foreach (Order order in orderList)
{
order.ProductName = returnProductName(order.ProductId);
}
if (!string.IsNullOrEmpty(searchValue))
{
orderList = orderList.Where(x => x.FullAddress.ToLower().Contains(searchValue.ToLower())
x.Id.ToString().Contains(searchValue.ToLower()) ||
x.OrderStatus.ToLower().Contains(searchValue.ToLower()) ||
x.ProductName.ToLower().Contains(searchValue.ToLower()) |||
x.Quantity.ToString().Contains(searchValue.ToLower()) ||
x.Cost.ToString().Contains(searchValue.ToLower()) ||
(!string.IsNullOrEmpty(x.TrackingNumber) && x.TrackingNumber.ToString().Contains(searchValue.ToLower()))
).ToList<Order>();
}
int totalRowsAfterFiltering = orderList.Count;
orderList = orderList.Skip(start).Take(length).ToList<Order>();
return Json(new { data = orderList, draw = Request.Form["draw"], recordsTotal = totalRows ,
recordsFiltered = totalRowsAfterFiltering});
}

Answer 1

I would perhaps consider updating the GetAll() method or creating another one which returns a dictionary.
In this case GetAllById() and then updating returnProductName which I would rename to GetProductName():
// Or whatever your type is
public Dictionary<int, List<Product>> GetAllById()
{
// your code..
return data
.GroupBy(x => x.Id)
.ToDictionary(x => x.Key, x => x.ToList());
}
public string GetProductName(int productId)
{
var products = _unitOfWork.Product.GetAllById();
return products[productId].FirstOrDefault(q => q.ProductName);
}