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UniqueConstraint Constructor (String, DataColumn())

Initializes a new instance of the UniqueConstraint class with the specified name and array of DataColumn objects.

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

'Declaration
Public Sub New ( _
	name As String, _
	columns As DataColumn() _
)

Parameters

name
Type: System.String

The name of the constraint.

columns
Type: System.Data.DataColumn()

The array of DataColumn objects to constrain.

The following example creates a DataTable with two columns, and adds a new UniqueConstraint to the ConstraintCollection.

Private Sub MakeTableWithUniqueConstraint()
    ' Create a DataTable with 2 DataColumns. 
    Dim dataTable As New DataTable("dataTable")
    Dim idColumn As New DataColumn( _
        "ID", System.Type.GetType("System.Int32"))
    Dim nameColumn As New DataColumn( _
        "Name", System.Type.GetType("System.String"))
    dataTable.Columns.Add(idColumn)
    dataTable.Columns.Add(nameColumn)

    ' Run procedure to create a constraint.
    AddUniqueConstraint(dataTable)

    ' Add one row to the table. 
    Dim dataRow As DataRow
    dataRow = dataTable.NewRow()
    dataRow("ID") = 1
    dataRow("Name") = "John"
    dataTable.Rows.Add(dataRow)

    ' Display the constraint name.
    Console.WriteLine(dataTable.Constraints(0).ConstraintName)

    ' Try to add an identical row, 
    ' which throws an exception. 
    Try
        dataRow = dataTable.NewRow()
        dataRow("ID") = 1
        dataRow("Name") = "John"
        dataTable.Rows.Add(dataRow)
    Catch ex As Exception
        Console.WriteLine("Exception Type: {0}", ex.GetType())
        Console.WriteLine("Exception Message: {0}", ex.Message)
    End Try 
End Sub 

Private Sub AddUniqueConstraint(ByVal dataTable As DataTable)
    ' Create the DataColumn array. 
    Dim dataColumns(1) As DataColumn
    dataColumns(0) = dataTable.Columns("ID")
    dataColumns(1) = dataTable.Columns("Name")

    ' Create the constraint on both columns. 
    Dim uniqueConstraint As UniqueConstraint = _
        New UniqueConstraint("idNameConstraint", dataColumns)
    dataTable.Constraints.Add(uniqueConstraint)
End Sub

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0
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