Conversion from type 'DBNull' to type 'String' is not valid

[gerryR com]

Hi All Slowly getting through my 1st asp.net page but need to pick your brains (again!) Basically I'm pulling data from an excel sheet, one of the thing's I'm doing with the data is making a url link, if there's text in column 2 then that's to be the text for the link, if there isn't then the text in column 1 is the text for the link. Problem is, as there doesn't necessarily have to be text in column 2 I'm getting a dbnull error. Below is my function and the asp code refering to that function. I know I need to put some error handeling but my big question is where? Is it within the function or within the asp link?

Function MakeLinkText(ByVal name As String, ByVal description As String) As String
If description = "" Then
name = name
else
name = description
end if
return name
End Function

<asp:TemplateField HeaderText="LinkText"><ItemTemplate><%# MakeLinkText(Container.Dataitem("title"), Container.Dataitem("refer to")) %></ItemTemplate></asp:TemplateField>

I did try on error resume nextwithin the function but still got the error (I realise thats very bad practice, I was just trying to narrow down the cause of the error. Appreciate a point in the right direction. Rgds gerryR

[Christian Graus]

Try if string.IsNullOrEmpty(description), assuming this is the point of error. In C#, you can do ?? string.Empty to turn null into an empty string.

Christian Graus No longer a Microsoft MVP, but still happy to answer your questions.

[NeverHeardOfMe]

In Visual Basic you can test for DbNull using If IsDbNull(whatever) Then... Howver, nb that you will need to re-write your function without explicitly defining the type - eg Assuming "name" is never null, but description might be:

Function MakeLinkText(ByVal name, ByVal description) As String
If IsDbNull(description) Then
Return CStr(name)
Else
Return CStr(description)
End If
End Function

[gerryR com]

Thanks once again Phil, workes perfectly! One question, if I leave the CStr out it still seems to work, is there some other reason for having it in other than just good code practice? (not that that's not reason enough!) Thanks again gerryR

[NeverHeardOfMe]

Well, not really... only that as the type is not explicitly defined it just takes care of any situation when you might call the same function from somewhere else with different data types...

[Abhishek Sur]

yes ... if you make Option Strict on then CStr is necessary.... :rose:

Abhishek Sur