DBNull Problem

[IndyGill]

Hi

I am having a problem with nulls in a database field. I have an object which produces a dataset, to which I then select a specific datarow. I want to check if a field in that datarow is null. However I keep getting this error "Cast from type 'DBNull' to type 'String' is not valid."

This is my code

Private Sub checkForNull(ByVal strArID As String)
rw = a.GetRow(strArID) 'this gets a specific row
If IsDBNull(rw.Area_ArID) Then
lable1.text = "DB is Null"
Else
label1.text = "DB has a value&quot
End If
End Sub

Thanks in advance

 

[rosenk]

What are the types of [tt]a[/tt] and [tt]rw[/tt]? (I don't know of a database-related class with a [tt]GetRow[/tt] function, offhand.)

 

[IndyGill]

rw is row from a datatable
a loads a dataset of

the row (rw) has several fields I know that some of them have a null value. So I select the rw.fieldname to select the value. But when I try write it out I get the "Cast from type 'DBNull' to type 'String' is not valid."

 

[rpeters74]

You can use a strong typed datarow. For each column, Foo, there exists a property, IsFooNull.

In your example:

If Not rw.IsArea_ArIDNull then
'do this
else
'do that
end if

 

[rosenk]

The way that I always checked if a value was null was:

[tt]If rw.Area_ArID Is DBNull.Value Then[/tt]

It seems to me that if it was doing a type conversion before, it might still have to for that. It's worth trying, though.

In case that doesn't help, do you know the actual, full, data types for [tt]a[/tt] and [tt]rw[/tt]? I understand that [tt]rw[/tt] is a row of data, but I want to look at the docs for the class.

 

[LV]

You can try

if(Convert.IsDbNull(somevalue))

 

[xtremeLogic]

I use the following function for converting null values:

Private Function DeNull(ByVal ThisValue As System.Object) As System.Object
     Return IIf(ThisValue Is DBNull.Value, "", ThisValue)
End Function

and an example of how i use it is:

Subject.Text = DeNull(Dr("Subject"))

where Dr is the name of my SQLDataReader

Hope that helps