DBNull Class
 

Represents a nonexistent value. This class cannot be inherited.

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


Syntax
[SerializableAttribute]
[ComVisibleAttribute(true)]
public sealed class DBNull : ISerializable, IConvertible
[SerializableAttribute]
[ComVisibleAttribute(true)]
public ref class DBNull sealed : ISerializable, IConvertible
[<Sealed>]
[<SerializableAttribute>]
[<ComVisibleAttribute(true)>]
type DBNull = 
    class
        interface ISerializable
        interface IConvertible
    end
<SerializableAttribute>
<ComVisibleAttribute(True)>
Public NotInheritable Class DBNull
	Implements ISerializable, IConvertible
Methods
NameDescription
System_CAPS_pubmethod Equals

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_pubmethod GetHashCode

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethod GetObjectData

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

System_CAPS_pubmethod GetType

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_pubmethod GetTypeCode

Gets the TypeCode value for DBNull.

System_CAPS_pubmethod ToString

Returns an empty string ( StringEmpty).(Overrides ObjectToString.)

System_CAPS_pubmethod ToString

Returns an empty string using the specified SystemIFormatProvider.

Fields
NameDescription
System_CAPS_pubfield System_CAPS_static Value

Represents the sole instance of the DBNull class.

Explicit Interface Implementations
NameDescription
System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToBoolean

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToByte

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToChar

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToDateTime

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToDecimal

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToDouble

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToInt16

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToInt32

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToInt64

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToSByte

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToSingle

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToType

This API supports the product infrastructure and is not intended to be used directly from your code. Converts the current DBNull object to the specified type.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToUInt16

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToUInt32

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

System_CAPS_pubinterface System_CAPS_privmethod IConvertibleToUInt64

This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException.

Remarks

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 DBNullValue member represents the sole DBNull object. DBNullValuecan 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 DBNullValue. These include the Visual Basic IsDBNull function, the ConvertIsDBNull method, the DataTableReaderIsDBNull method, and the IDataRecordIsDBNull method.

Do not confuse the notion of null in an object-oriented programming language with a DBNull object. In an object-oriented programming language, null means the absence of a reference to an object. DBNull represents an uninitialized variant or nonexistent database column.

Examples

The following example calls the DBNull.Value.Equals method to determine whether a database field in a contacts database has a valid value. If it does, the field value is appended to the string output in a label.

private void OutputLabels(DataTable dt)
{
   string label; 

   // Iterate rows of table
   foreach (DataRow row in dt.Rows)
   {
      int labelLen;
      label = String.Empty;
      label += AddFieldValue(label, row, "Title");
      label += AddFieldValue(label, row, "FirstName");
      label += AddFieldValue(label, row, "MiddleInitial");
      label += AddFieldValue(label, row, "LastName");
      label += AddFieldValue(label, row, "Suffix");
      label += "\n";
      label += AddFieldValue(label, row, "Address1");
      label += AddFieldValue(label, row, "AptNo");
      label += "\n";
      labelLen = label.Length;
      label += AddFieldValue(label, row, "Address2");
      if (label.Length != labelLen)
         label += "\n";
      label += AddFieldValue(label, row, "City");
      label += AddFieldValue(label, row, "State");
      label += AddFieldValue(label, row, "Zip");
      Console.WriteLine(label);
      Console.WriteLine();
   }
}

private string AddFieldValue(string label, DataRow row, 
                             string fieldName) 
{                                
   if (! DBNull.Value.Equals(row[fieldName])) 
      return (string) row[fieldName] + " ";
   else
      return String.Empty;
}
Private Sub OUtputLabels(dt As DataTable)
   Dim label As String 

   ' Iterate rows of table
   For Each row As DataRow In dt.Rows
      Dim labelLen As Integer
      label = String.Empty
      label += AddFieldValue(label, row, "Title")
      label += AddFieldValue(label, row, "FirstName")
      label += AddFieldValue(label, row, "MiddleInitial")
      label += AddFieldValue(label, row, "LastName")
      label += AddFieldValue(label, row, "Suffix")
      label += vbCrLf
      label += AddFieldValue(label, row, "Address1")
      label += AddFieldValue(label, row, "AptNo")
      label += vbCrLf
      labelLen = Len(label)
      label += AddFieldValue(label, row, "Address2")
      If Len(label) <> labelLen Then label += vbCrLf
      label += AddFieldValue(label, row, "City")
      label += AddFieldValue(label, row, "State")
      label += AddFieldValue(label, row, "Zip")
      Console.WriteLine(label)
      Console.WriteLine()
   Next
End Sub

Private Function AddFieldValue(label As String, row As DataRow, _
                          fieldName As String) As String
   If Not DbNull.Value.Equals(row.Item(fieldName)) Then
      Return CStr(row.Item(fieldName)) & " "
   Else
      Return Nothing
   End If
End Function
Version Information
Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Thread Safety

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

Return to top