DBNull Class

Represents a nonexistent value. This class cannot be inherited.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public NotInheritable Class DBNull _
	Implements IConvertible

The DBNull type exposes the following members.

  NameDescription
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetTypeCodeGets the TypeCode value for DBNull.
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns an empty string (String.Empty). (Overrides Object.ToString.)
Public methodToString(IFormatProvider)Returns an empty string using the specified System.IFormatProvider.
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  NameDescription
Public fieldStatic memberValueRepresents the sole instance of the DBNull class.
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  NameDescription
Explicit interface implemetationPrivate methodIConvertible.ToBooleanInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToByteInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToCharInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToDateTimeInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToDecimalInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToDoubleInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToInt16Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToInt32Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToInt64Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToSByteInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToSingleInfrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToTypeInfrastructure. Converts the current DBNull object to the specified type.
Explicit interface implemetationPrivate methodIConvertible.ToUInt16Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToUInt32Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
Explicit interface implemetationPrivate methodIConvertible.ToUInt64Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.
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The DBNull class represents a nonexistent value. In a database, for example, a column in a row of a table might not contain any data whatsoever. That is, the column is considered to not exist at all instead of merely not having a value. A DBNull object represents the nonexistent column. Additionally, COM interop uses the DBNull class to distinguish between a VT_NULL variant, which indicates a nonexistent value, and a VT_EMPTY variant, which indicates an unspecified value.

The DBNull type is a singleton class, which means only one DBNull object exists. The DBNull.Value member represents the sole DBNull object. DBNull.Value can be used to explicitly assign a nonexistent value to a database field, although most ADO.NET data providers automatically assign values of DBNull when a field does not have a valid value. You can determine whether a value retrieved from a database field is a DBNull value by passing the value of that field to the DBNull.Value.Equals method. However, some languages and database objects supply methods that make it easier to determine whether the value of a database field is DBNull.Value. These include the Visual Basic IsDBNull function and the Convert.IsDBNull method.

Do not confuse the notion of Nothing in an object-oriented programming language with a DBNull object. In an object-oriented programming language, Nothing means the absence of a reference to an object. DBNull represents an uninitialized variant or nonexistent database column.

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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