How to handle null in LINQ query for nullable int if value not found

Question

Here i am using simple list and one of the ageto string column is null

I am check in linq query if value not found then to return null. But value cannot be null error is coming up

var list = new[]
    {
        new { AgeFrom = "0", AgeTo="24"},
        new { AgeFrom = "70", AgeTo= (string)null}
    }.ToList();


var result = from r in list 
                 select new EmployeeDTO 
         {
           //AgeFrom Column is int? in DTO  
           AgeFrom = Convert.ToInt32(r.AgeFrom),
           //AgeTo Column is int? in DTO    
           AgeTo = Convert.ToInt32(r.AgeTo ?? null)
         }

Doesn't matter what it is in the DTO, Convert.ToInt32() does not take a null parameter — Afnan Makhdoom
– Afnan Makhdoom, Commented Aug 30, 2017 at 18:22
This code works for me as is, I don't understand the problem. — Yuriy Faktorovich
– Yuriy Faktorovich, Commented Aug 30, 2017 at 18:24

Afnan Makhdoom · Accepted Answer · 2017-08-30 18:46:48Z

3

Try this:

AgeTo = String.IsNullOrEmpty(r.AgeTo) ? (int?)null : (int?)Convert.ToInt32(r.AgeTo);

Which makes your code:

    var list = new[]
    {
        new { AgeFrom = "0", AgeTo="24"},
        new { AgeFrom = "70", AgeTo= (string)null}
    }.ToList();


    var result = from r in list 
                 select new EmployeeDTO 
      {
        //AgeFrom Column is int? in DTO  
        AgeFrom = Convert.ToInt32(r.AgeFrom),
        //AgeTo Column is int? in DTO    
        String.IsNullOrEmpty(r.AgeTo) ? (int?)null : (int?)Convert.ToInt32(r.AgeTo)
      };

Convert.ToInt32 can not convert null to an integer, that will always throw an exception.

edited Aug 30, 2017 at 18:46

answered Aug 30, 2017 at 18:23

Afnan Makhdoom

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4 Comments

user1030181 Over a year ago

Getting this error Type of conditional expression cannot be determined because there is no implicit conversion between '<null>' and 'int'

BurnsBA Over a year ago

add explicit cast to the values being set: (int?)null : (int?)Convert.ToInt32(r.AgeTo)

Afnan Makhdoom Over a year ago

Yea, looked over the nullable property, thanks @BurnsBA

user1030181 Over a year ago

Getting value cannot be null error ...Argument Null Exception

Kirk Larkin · Accepted Answer · 2017-08-30 18:23:29Z

1

One option would be to change:

AgeTo = Convert.ToInt32(r.AgeTo ?? null)

to:

AgeTo = r.AgeTo != null ? Convert.ToInt32(r.AgeTo) : null

The statement r.AgeTo ?? null is an example of the null-coalescing operator, which, in your case, is essentially saying that if r.AgeTo is null, then use null instead. As this isn't what you were trying to achieve, you are in fact passing null into Convert.ToInt32, which is causing your error.

answered Aug 30, 2017 at 18:23

Kirk Larkin

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