C# in a Nutshell, Second Edition

Name

DBNull

Synopsis

DBNull indicates the absence of information, typically in a database application in which a field does not contain any data. The types in the System.Data.SqlTypes namespace have built-in support for DBNull.

Note that Value is not the same as the null keyword in C#. The null keyword can be used to release an object by clearing the reference. System.DBNull.Value, on the other hand, is a reference to a special value (a member of the singleton class DBNull) that is used to indicate missing information.

This class has some other uses, namely in COM Interop, in which it represents a VT_EMPTY variant (as opposed to a VT_NULL variant, which is a null reference).

public sealed class DBNull : System.Runtime.Serialization.ISerializable, IConvertible {
// Public Static Fields
   public static readonly DBNull Value;
// Public Instance Methods
   public void GetObjectData(System.Runtime.Serialization.SerializationInfo info,
        System.Runtime.Serialization.StreamingContext context)
// implements ISerializable
   public TypeCode GetTypeCode( );        
// implements IConvertible
   public override string ToString( );    
// overrides object
   public string ToString(IFormatProvider provider); 
// implements IConvertible
}