Cast from type 'DBNull' to type 'String' is not valid.

[Drstein99]

How do I deal with null values in tables? If i'm getting information from a table (all over the program) and in one record in one field might be a random DBNULL, whats the best way to cast this into a string?

 

"Cast from type 'DBNull' to type 'String' is not valid."

 

 

line of code:

 

sTemp2 = esEmpTable.Rows(0).Item("middle name")

[jfackler]

If (esEmpTable.Rows(0).Item("middle name")GetType.ToString)<> "System.DBNull" Then
sTemp2 = cstr(esEmpTable.Rows(0).Item("middle name"))
Else: sTemp2 = "No value set"
End If

Edited October 14, 2003 by jfackler

[Drstein99]

Yep. That fixed it. I added the code to my generic code to query data for the whole program. If it's a dbnull, then it makes it " ", so if it ever goes to write the data back then it won't be null and cause error.

[Volte]

A possibly more efficient way to do it (plus shorter) is like this:

If esEmpTable.Rows(0).Item("middle name") <> Convert.DBNull Then sTemp2 = esEmpTable.Rows(0).Item

I would avoid string comparison wherever possible due to the terrible inefficiency and speed issues.

[Drstein99]

That is shorter, and you definately showed me a nicer way of accomplishing what I need thank you. BTW - I'm just trying to replace the data with a space in event of null

 

If esEmpTable.Rows(0).Item("middle name") = Convert.DBNull Then esEmpTable.Rows(0).Item("middle name") = " "

 

Thank you very much.

[Nerseus]

Slightly off-topic:

I've never seen Convert.DBNull - is that VB-specific, or just another way to get at DBNull? In C# it's System.DBNull.Value.

 

I'm just wondering if it's like int and Int32 in C# or Integer and Int32 in VB.NET (the same object, just used two different ways - or 4 if you count different languages).

 

-nerseus

[Volte]

I'm using it in my C# app right now, so it's not VB specific. I think the idea is that it represents an object rather than a value, so it can be used as such.

[Jerod]

Here's the way I prefer to check this, for what its worth:

 

<vb>

if ISDBNull(esEmpTable.Rows(0).Item("middle name")) then sTemp2 = esEmpTable.Rows(0).Item

</vb>

[Jerod]

Sorry, misinterpretation. Should be:

 

if ISDBNull(esEmpTable.Rows(0).Item("middle name")) then sTemp2 = " "

[Volte]

Now that one is VB.NET specific. As a general rule, if you are using a standalone function (i.e. ThisFunction(params) rather than Class.ThisFunction(params)) that is built in to the framework, there is a good chance it is for VB6 compatability. With .NET, almost all functions are built into the classes they modify: stringobject.IndexOf() has replaced InStr(), for example. Nothing stands out on its own except the VB6 compatability library.

 

I really hope Microsoft does away with it in the next .NET, though I really don't see it happening.

[Drstein99]

I agree. I just started .net 2 months ago, from using VB6 and this new way of doing things has slowed me a down alot. But if microsoft does decide to change things I'm not sure I'm gonna be so quick to upgrade, as I get used to using one thing I'm forced to learn a new way with these upgrades.