Question

I’ve got this problem, I have a table for purchases

Purchases(Date DateTime, Number string)

I want is to create a new record, so I need the Max(Number), the problem here is that Number is a string, I’ve tried

Purchases.Select(X=>int.Parse(X.Number)).Max()

but it could throw an exception, I’ve create a custom ToInt() extension so when I use

Purchases.Select(X=>X.Number.ToInt()).Max()

it throws an exception saying that my ToInt() can’t be used with linq query same as the famous ToString()

so my question is : is there a way to cast a string to int in linq query & handling exceptions at the same time or to integrate custom functions to a linq query !!

and this’s my extension

    public static int ToInt(this string s)
    {
        try
        {
            return int.Parse(s);
        }
        catch
        {
        }
        return 0;
    }

Answer 1

First way:

var numbers = Purchases.Select(x => x.Number).ToList();

int temp;
int max = numbers.Select(n => int.TryParse(n, out temp) ? temp : 0).Max();

Console.WriteLine("Max: {0}", max);

Second way:

int temp2;
int max2 = Purchases.Select(x => x.Number).ToList().Select(n => int.TryParse(n, out temp2) ? temp2 : 0).Max();

Console.WriteLine("Max 2: {0}", max2);

The key is the .ToList() in those two ways. It gets all the string data from the database, so when you call int.TryParse on the results, the database query has already been run, so it is using pure CLR code, and not trying to convert int.TryParse into a SQL query. I made an EF context in one of my Sandbox projects and verified this works.