August 2003
Intermediate to advanced
928 pages
32h 1m
English
DBNull
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.SerializationInfoinfo, System.Runtime.Serialization.StreamingContextcontext) // implements ISerializable public TypeCode GetTypeCode( ); // implements IConvertible public override string ToString( ); // overrides object public string ToString(IFormatProviderprovider); // implements IConvertible }