Conversion from type 'DBNull' to type 'Integer' is not valid in designer

Question

I have a code below in an Entity Class. It throws exception in the Entity.Designer.vb saying the value Amount in Table Patient is DbNull.

    If _patientDetails.ID > 0 Then
        If _patientDetails.Amount = EntityEnums.Patient.Existing
            Then                          
               _patientDetails.SetAmountNull()
        End If
    Catch ex As Exception
        _patientDetails.SetAmountNull()
    End Try

End If

It goes to the "Return" line as below and throws exception.

Public Property Amount() As Integer
    Get
        Try 
            Return CType(Me(Me.tablePatient.AmountIDColumn),Integer)
        Catch e As Global.System.InvalidCastException
            Throw New Global.System.Data.StrongTypingException("The value for column 'AmountIDColumn' in table 'Patient' is D"& _ 
                    "BNull.", e)
        End Try
    End Get
    Set
        Me(Me.tablePatient.AmountIDColumn) = value
    End Set
End Property

Exception Details are

A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll

Additional information: Conversion from type 'DBNull' to type 'Integer' is not valid.

@Plutonix: Hi Plutonix, I just changed some names, that's all. It is the error that dbnull to integer casting. Everywhere they have this but I am afraid only in this place it throws error because i used this column. Any suggestions please to resolve? — Jasmine, Dec 30 '15 at 22:27
No. That If block for `If _patientDetails.Amount ` is malformed. Lines dont start with `Then` — Ňɏssa Pøngjǣrdenlarp, Dec 30 '15 at 22:29
@Plutonix: THis is what is there in my project. And as you suspect, it is exactly the location where it throws exception but when the control comes to "First If block". Obviously it is trying to access that property and in the property, it throws exception. — Jasmine, Dec 30 '15 at 22:31

score 1 · Answer 1 · answered Dec 30 '15 at 22:58

Ultimately, indeed: you can't cast from DBNull to integer. You will need to check for DBNull, and special-case whatever you want to happen in that scenario. Perhaps treat it as 0 or -1, perhaps do something different: only you know.

If this was C#, I would use:

var val = tablePatient.AmountIDColumn;
if(val is DBNull) {
    // special-case; return 0, perhaps
} else {
    // cast, etc
    return (int)val; // or Convert.ChangeType, if it is something exotic
}

(my VB-foo is weak, so I'll leave the translation as an exercise for the reader)

score 0 · Answer 2 · answered Dec 31 '15 at 08:34

Try this:

    If _patientDetails.ID > 0 Then
        If (Not _patientDetails.IsAmountNull) AndAlso (_patientDetails.Amount = EntityEnums.Patient.Existing) Then
            _patientDetails.SetAmountNull()
        End If
    End If          

    Catch ex As Exception
        _patientDetails.SetAmountNull()
    End Try

Conversion from type 'DBNull' to type 'Integer' is not valid in designer

2 Answers2