Question

I am building a JSON string and in the rows section, I have two values that I want to build and pass in the JSON string which are calculated by a helper function. I am wondering if there a way to call this helper function once, and return back an array of values (two in my case) so I don’t have to call the helper function twice (and avoid hitting the database twice).

Example Code

            rows = (
                from tempItem in pagedQuery.ToList()
                select new
                {
                    cell = new string[] {                    
                        tempItem.Name,
                        tempItem.Regular,
                        HelperFunction.GetPrice(tempItem.ID, false).ToString(),
                        tempItem.Premium,
                        HelperFunction.GetPrice(tempItem.ID, true).ToString(),
                    }
                }).ToArray()

Example Function:

public decimal GetPrice(int ID, bool Premium)
{
  Item item = databaseCallToGetPrice(ID).first();

  if (Premium)
      return item.ExamplePrice;
  else
      return item.PremiumExamplePrice;
}

So what I am asking is in my example I call the Helper function twice, is there a way to call on it just the once and then return back an array that I can somehow persist and then use twice.

Answer 1

Return a Tuple<decimal, decimal> from the function:

public Tuple<decimal, decimal> GetPrices(int ID)
{
    Item item = databaseCallToGetPrice(ID).First();
    return Tuple.Create(item.ExamplePrice, item.PremiumExamplePrice);
}

Then use that:

rows = (
        from tempItem in pagedQuery.ToList()
        let prices = HelpererFunction.GetPrices(tempItem.ID)
        select new
        {
            cell = new string[] {                    
                tempItem.Name,
                tempItem.Regular,
                prices.Item1.ToString(),
                tempItem.Premium,
                prices.Item2.ToString(),
            }
        }).ToArray()

IMHO a tuple is better than a simple array because you’re guaranteed to get two and only two items back from the function.

---

If you want to be even clearer, you can create a struct

public struct Prices
{
    public decimal PremiumPrice, Price;       

    public Prices(decimal premium, decimal price)
    {
        PremiumPrice = premium;
        Price = price;
    } 
}

then return that from the helper function

public Prices GetPrices(int ID)
{
    Item item = databaseCallToGetPrice(ID).First();
    return new Prices(item.PremiumExamplePrice, item.ExamplePrice);
}

and use that:

rows = (
        from tempItem in pagedQuery.ToList()
        let prices = HelpererFunction.GetPrices(tempItem.ID)
        select new
        {
            cell = new string[] {                    
                tempItem.Name,
                tempItem.Regular,
                prices.Price.ToString(),
                tempItem.Premium,
                prices.PremiumPrice.ToString(),
            }
        }).ToArray()