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DataColumn Constructor (String, Type, String, MappingType)

Initializes a new instance of the DataColumn class using the specified name, data type, expression, and value that determines whether the column is an attribute.

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

'Declaration
Public Sub New ( _
	columnName As String, _
	dataType As Type, _
	expr As String, _
	type As MappingType _
)
'Usage
Dim columnName As String 
Dim dataType As Type 
Dim expr As String 
Dim type As MappingType 

Dim instance As New DataColumn(columnName, _
	dataType, expr, type)

Parameters

columnName
Type: System.String

A string that represents the name of the column to be created. If set to Nothing or an empty string (""), a default name will be specified when added to the columns collection.

dataType
Type: System.Type

A supported DataType.

expr
Type: System.String

The expression used to create this column. For more information, see the Expression property.

type
Type: System.Data.MappingType

One of the MappingType values.

ExceptionCondition
ArgumentNullException

No dataType was specified.

The type argument sets the ColumnMapping property. The property specifies how a DataColumn is mapped when a DataSet is transformed into an XML document. For example, if the column is named "fName," and the value it contains is "Bob," and type is set to MappingType.Attribute, the XML element would be as follows:

<Name fName = 'Bob'/>

For more information about how columns are mapped to elements or attributes, see the ColumnMapping property.

The following example constructs a computed column.

Private Sub CreateComputedColumn(ByVal table As DataTable)
    Dim column As DataColumn
    Dim decimalType As System.Type = _
        System.Type.GetType("System.Decimal")

    ' The expression multiplies the "Price" column value by the  
    ' "Quantity" to create the "Total" column. 
    Dim expression As String = "Price * Quantity" 

    ' Create the column, setting the type to Attribute.
    column = New DataColumn("Total", decimalType, _
        expression, MappingType.Attribute)

    ' Set various properties.
    column.AutoIncrement = False
    column.ReadOnly = True 

    ' Add the column to a DataTable object's DataColumnCollection.
    DataSet1.Tables("OrderDetails").Columns.Add(column)
End Sub

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
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