VBSciptEngine - DBNULL is returned as Nothing

[DanielGerlach2]

I have a function that returns the value of a field for an record which represents a data record from a table in the MSSQL server.

e.g.
Class Record
...
Function Value(Field as String) as Object
...
End Class

When using the MSScriptcontrol, DBNULL is returned for empty fields.

Sub Main
If ISDBNULL(Record.Value("Field1")) Then
...
End If
End Sub

Now when you run the same script code via VBSciptEngine, Nothing is returned.

Is there a setting or switch to get the expected return?

[ClearScriptLib]

Hi @DanielGerlach2,

ClearScript converts .NET's DBNull.Value to VBScript's Null. You can use VBScript's IsNull function to test for it. To accommodate your existing script code, you could define ISDBNULL as an alias for IsNull.

Good luck!

[DanielGerlach2]

Thank you very much for the quick answer.
I have now broken down the behavior into a test project and made it available as a ZIP.

I still think it's an error because it should actually return DBNULL, but it arrives as Nothing.

https://www.file-upload.net/download-15445692/tstClearscript_627.zip.html

[ClearScriptLib]

Thanks for posting your test application!

I still think it's an error because it should actually return DBNULL, but it arrives as Nothing.

NET's COM Interop layer treats DBNull.Value as a special case, marshaling it in a form that JScript and VBScript recognize as null. That makes sense because null is a native and easy-to-use value in both languages.

Where ClearScript differs is in the handling of null when it's passed back to the host. ClearScript converts it to .NET's null/Nothing because that seems like a natural mapping, at least for C# (null → null). Nevertheless, we agree that lossless round tripping for DBNull.Value might be preferable.

We'll take a closer look at this for ClearScript's next release.

Thanks!