Represents a nonexistent value. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
<[%$TOPIC/934efkk6_en-us_VS_110_2_0_0_0_0%]> _
<[%$TOPIC/934efkk6_en-us_VS_110_2_0_0_0_1%](True)> _
Public NotInheritable Class DBNull _
Implements [%$TOPIC/934efkk6_en-us_VS_110_2_0_0_0_2%], [%$TOPIC/934efkk6_en-us_VS_110_2_0_0_0_3%]
[[%$TOPIC/934efkk6_en-us_VS_110_2_0_1_0_0%]]
[[%$TOPIC/934efkk6_en-us_VS_110_2_0_1_0_1%](true)]
public sealed class DBNull : [%$TOPIC/934efkk6_en-us_VS_110_2_0_1_0_2%],
[%$TOPIC/934efkk6_en-us_VS_110_2_0_1_0_3%]
[[%$TOPIC/934efkk6_en-us_VS_110_2_0_2_0_0%]]
[[%$TOPIC/934efkk6_en-us_VS_110_2_0_2_0_1%](true)]
public ref class DBNull sealed : [%$TOPIC/934efkk6_en-us_VS_110_2_0_2_0_2%],
[%$TOPIC/934efkk6_en-us_VS_110_2_0_2_0_3%]
[<[%$TOPIC/934efkk6_en-us_VS_110_2_0_3_0_0%]>]
[<[%$TOPIC/934efkk6_en-us_VS_110_2_0_3_0_1%]>]
[<[%$TOPIC/934efkk6_en-us_VS_110_2_0_3_0_2%](true)>]
type DBNull =
class
interface [%$TOPIC/934efkk6_en-us_VS_110_2_0_3_0_3%]
interface [%$TOPIC/934efkk6_en-us_VS_110_2_0_3_0_4%]
end
The DBNull type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | Equals(Object) | Determines whether the specified object is equal to the current object. (Inherited from Object.) |
![]() | GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
![]() | GetObjectData | Implements the ISerializable interface and returns the data needed to serialize the DBNull object. |
![]() | GetType | Gets the Type of the current instance. (Inherited from Object.) |
![]() | GetTypeCode | Gets the TypeCode value for DBNull. |
![]() | ToString | Returns an empty string ( StringEmpty). (Overrides ObjectToString.) |
![]() | ToString(IFormatProvider) | Returns an empty string using the specified SystemIFormatProvider. |
| Name | Description | |
|---|---|---|
![]() | IConvertibleToBoolean | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToByte | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToChar | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToDateTime | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToDecimal | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToDouble | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToInt16 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToInt32 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToInt64 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToSByte | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToSingle | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToType | Infrastructure. Converts the current DBNull object to the specified type. |
![]() | IConvertibleToUInt16 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToUInt32 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
![]() | IConvertibleToUInt64 | Infrastructure. This conversion is not supported. Attempting to make this conversion throws an InvalidCastException. |
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. DBNullValue 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 DBNullValue. These include the Visual Basic IsDBNull function, the ConvertIsDBNull method, the DataTableReaderIsDBNull method, and the IDataRecordIsDBNull method.
Do not confuse the notion of in an object-oriented programming language with a DBNull object. In an object-oriented programming language, means the absence of a reference to an object. DBNull represents an uninitialized variant or nonexistent database column.
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 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
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;
}
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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