Visual Basic 2005 in a Nutshell (In a Nutshell (OReilly))

IsDBNull Function

Class

Microsoft.VisualBasic.Information

Syntax

Dim result As Boolean = IsDBNull(expression)

expression (required; any)

The expression to be evaluated against System.DBNull

Description

The IsDBNull function determines whether expression evaluates to System.DbNull (true) or not (False).

Usage at a Glance

  • DbNull is not the same as Nothing or an empty string. DbNull is used to denote a missing or nonexistent value, and it is used primarily in the context of database field values.

  • Because of the way that VB deals with expressions containing DBNull, you cannot simply compare a variable to DBNull, as in:

    If (someVariable = DbNull) Then

    You must make the comparison using the IsDbNull function.

    If (IsDBNull(someVariable) = True) Then

Version Differences

  • The IsDBNull function is new with VB under .NET.

  • Visual Basic 2005 includes a new IsNullOrEmpty method as part of the String data type that may better meet your needs.

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