Represents a nonexistent value. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
Thetype exposes the following members.
|Equals(Object)||Determines whether the specified Object is equal to the current Object. (Inherited from Object.)|
|Finalize||Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)|
|GetHashCode||Serves as a hash function for a particular type. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|GetTypeCode||Gets the TypeCode value for .|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|ToString()||Returns an empty string (String.Empty). (Overrides Object.ToString().)|
|ToString(IFormatProvider)||Returns an empty string using the specified System.IFormatProvider.|
|IConvertible.ToBoolean||Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.|
|IConvertible.ToByte||Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.|
|IConvertible.ToChar||Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.|
|IConvertible.ToType||Infrastructure. Converts the current object to the specified type.|
The 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 object represents the nonexistent column. Additionally, COM interop uses the class to distinguish between a VT_NULL variant, which indicates a nonexistent value, and a VT_EMPTY variant, which indicates an unspecified value.
The type is a singleton class, which means only one object exists. The DBNull.Value member represents the sole 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 when a field does not have a valid value. You can determine whether a value retrieved from a database field is a 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 null in an object-oriented programming language with a object. In an object-oriented programming language, null means the absence of a reference to an object. represents an uninitialized variant or nonexistent database column.
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