Conversion from string "" to type 'Integer' is not valid - ASP.net using VB

Question

this error keeps showing on this line of code

ApplicantSett.Nationality1 = IIf(IsDBNull(ds.Tables("Applicant").Rows(i)("Nationality1").ToString) Or IsNothing(ds.Tables("Applicant").Rows(i)("Nationality1").ToString),
                               Nothing, CInt(ds.Tables("Applicant").Rows(i)("Nationality1").ToString))

the variable Nationality1 is an Integer and it is null in the database so it is not converting. what should I do?

You are using tostring, in essential trying to match a string with an integer. Parse Nationality1 to an integer in stead of doing tostring — Tikkes
– Tikkes, Commented Jul 18, 2017 at 7:13
i got another error: Conversion from type 'DBNull' to type 'String' is not valid. — Patricia Matar
– Patricia Matar, Commented Jul 18, 2017 at 7:23
Remove ToString when checking both DBNull & Nothing conditions: IIf(IsDBNull(ds.Tables("Applicant").Rows(i)("Nationality1")) Or IsNothing(ds.Tables("Applicant").Rows(i)("Nationality1")), Nothing, CInt(ds.Tables("Applicant").Rows(i)("Nationality1").ToString)). — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Jul 18, 2017 at 7:27
The test of IsDbNull on a ToString value is wrong: The ToString has converted a possible DbNull value to an empty string, which is not DbNull anymore. So this will always return False. Solution: remove the .ToString. — Hans Keﬆing
– Hans Keﬆing, Commented Jul 18, 2017 at 8:24
You don't need to test for IsNothing, a DataRow field will never be Nothing, but DbNull. Plus when it were Nothing, then the ToString would crash (NullReferenceException). — Hans Keﬆing
– Hans Keﬆing, Commented Jul 18, 2017 at 8:25

Thiam Hooi · Accepted Answer · 2017-07-18 07:42:02Z

1

Dim nationality As Object = ds.Tables("Applicant").Rows(i)("Nationality1")

If (nationality IsNot Nothing 
AndAlso nationality <> System.DBNull.Value 
AndAlso Not System.String.IsNullOrEmpty(nationality.ToString()) Then
    Dim output As Integer
    If (System.Int32.TryParse(value, output)) Then
        ApplicantSett.Nationality1 = output
    End If
End If

If you have a lots of returned values which are needed to be parsed, then you may write your own Parser to parse the value in one line of code.

Integer.Parse vs. CInt - https://stackoverflow.com/a/423910/2046832

answered Jul 18, 2017 at 7:42

Thiam Hooi

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