using int.TryParse with Queryable and expression

Question

I am new to Expressions in c#.

Expression code

var parameter = Expression.Parameter(typeof(int), "param");
var constant = Expression.Constant(5, typeof(int));
var equal = Expression.Equal(parameter, constant);
var lambdaExpression = Expression.Lambda<Func<int, bool>>(equal, parameter);
var compiledExpression = lambdaExpression.Compile();

Query contains a string value and I want to apply expresion only if the value is convertible to int

int test;
query = query.Where(i => int.TryParse(i.Key, out test) && compiledExpression(test));

This returns an error saying int.TryParse is not supported. Any way to solve this?

If it is a LINQ to SQL query, then you cannot use a compiled expression. — Yacoub Massad
– Yacoub Massad, Commented Aug 25, 2016 at 21:26

SledgeHammer · Accepted Answer · 2016-08-25 21:57:24Z

1

You can't use out parameters there.

1) var v = q.Where(x => x.All(c => c >= '0' && c <= '9'));
2) use regex instead of All
3) write a simple method that calls Int32.Parse and just returns a bool to hide the out param

for #3:

    static bool SafeIntParse(string s)
    {
        int n;
        return Int32.TryParse(s, out n);
    }

    var v = q.Where(x => SafeIntParse(x));

The SafeIntParse() method is, of course, a separate static method.

EDIT:

for the regex method:

        Regex regex = new Regex("^\\d+$", RegexOptions.Compiled);
        var v = q.Where(x => regex.Match(x).Success);

Of course, make the regex object a static object of the class.

edited Aug 25, 2016 at 21:57

answered Aug 25, 2016 at 21:26

SledgeHammer

7,7668 gold badges54 silver badges100 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user3469799 Over a year ago

Part (2) is not clear. I tried (3) but it throws error lambda expressions are not allowed @sledgehammer

user3469799 Over a year ago

Sorry, if I was not clear. What I meant was can please elaborate Part2 use regex instead of all. Where and how? @sledgehammer

Cristian Quesada · Accepted Answer · 2024-03-16 01:24:45Z

0

You can implement your own function to get the value, int.TryParse returns 0 by default if the string cannot be converted.

Here you have

private decimal GetDecimal(string value)
{
    if(decimal.TryParse(value, out decimal result))
        return result;
    return 0;
}

answered Mar 16, 2024 at 1:24

Cristian Quesada

235 bronze badges

1 Comment

Gert Arnold Over a year ago

Please see the comments. It's a query that should be translated into SQL. Calling GetDecimal instead of int.TryParse isn't supported either.

Collectives™ on Stack Overflow

using int.TryParse with Queryable and expression

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related