System.DBNull Class

Summary

Represents a null value.

C# Syntax:

[Serializable] public sealed class DBNull : ISerializable, IConvertible

Public static (non-instance) members of this type are safe for multithreaded operations. Instance members are not guaranteed to be thread-safe.

This class is used to indicate the absence of a known value, typically in a database application.

In database applications, a null object is a valid value for a field. This class differentiates between a null value (a null object) and an uninitialized value (the DBNull.Value instance). For example, a table can have records with uninitialized fields. By default, these uninitialized fields have the DBNull value.

This class is also used in COM Interop to distinguish between a VT_NULL variant, which is associated with a null object, and a VT_EMPTY variant, which is associated with the DBNull.Value instance.

DBNull is never equal to anything.

DBNull is a singleton class, which means only one instance of this class can exist. That sole instance is DBNull.Value.

Data intensive applications accessing SQL databases must use the System.Data.SqlTypes classes, which have inherent support for null values.

System Namespace | Convert.DBNull | Convert.IsDBNull | VarEnum | System.Data.SqlTypes

System.DBNull Member List:

Public Fields

Value

Represents the sole instance of the DBNull class.

Public Methods

Equals (inherited from System.Object)	See base class member description: System.Object.Equals Derived from System.Object, the primary base class for all objects.
GetHashCode (inherited from System.Object)	See base class member description: System.Object.GetHashCode Derived from System.Object, the primary base class for all objects.
GetObjectData	Implements the ISerializable interface and returns the data needed to serialize the DBNull object.
GetType (inherited from System.Object)	See base class member description: System.Object.GetType Derived from System.Object, the primary base class for all objects.
GetTypeCode
ToString	Overloaded: ToString() Overridden: Returns an empty string ( String.Empty).
ToString	Overloaded: ToString(IFormatProvider provider) Returns an empty string using the specified IFormatProvider.

Protected Methods

Finalize (inherited from System.Object)	See base class member description: System.Object.Finalize Derived from System.Object, the primary base class for all objects.
MemberwiseClone (inherited from System.Object)	See base class member description: System.Object.MemberwiseClone Derived from System.Object, the primary base class for all objects.

Hierarchy:

• System.Object
• System.DBNull

System.DBNull Member Details

Summary

Represents the sole instance of the DBNull class.

C# Syntax:

public static readonly DBNull Value;

DBNull is a singleton class, which means only this instance of this class can exist.

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Inherited
See base class member description: System.Object.Equals

C# Syntax:

public virtual bool Equals(    object obj );

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.Finalize

C# Syntax:

~DBNull();

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.GetHashCode

C# Syntax:

public virtual int GetHashCode();

For more information on members inherited from System.Object click on the link above.

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Summary

Implements the ISerializable interface and returns the data needed to serialize the DBNull object.

C# Syntax:

public void GetObjectData(    SerializationInfo info,    StreamingContext context );

info

A SerializationInfo object containing information required to serialize the DBNull object.

context

A StreamingContext object containing the source and destination of the serialized stream associated with the DBNull object.

Exceptions

Exception Type	Condition
ArgumentNullException	info is null.

Implements:

ISerializable.GetObjectData

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Inherited
See base class member description: System.Object.GetType

C# Syntax:

public Type GetType();

For more information on members inherited from System.Object click on the link above.

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Summary

Gets the TypeCode value for DBNull.

C# Syntax:

public TypeCode GetTypeCode();

Return Value:

The TypeCode value for DBNull, which is TypeCode.DBNull.

Implements:

IConvertible.GetTypeCode

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Inherited
See base class member description: System.Object.MemberwiseClone

C# Syntax:

protected object MemberwiseClone();

For more information on members inherited from System.Object click on the link above.

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Summary

Returns an empty string ( String.Empty).

C# Syntax:

public override string ToString();

Return Value:

An empty string ( String.Empty).

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Summary

Returns an empty string using the specified IFormatProvider.

C# Syntax:

public string ToString(    IFormatProvider provider );

provider

The IFormatProvider to be used to format the return value. -or-

null to obtain the format information from the current locale setting of the operating system.

-or-

null to obtain the format information from the current locale setting of the operating system.

Return Value:

An empty string ( String.Empty).

Implements:

IConvertible.ToString

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