UniqueConstraint Class (System.Data)

.NET Framework Class Library

UniqueConstraint Class

Represents a restriction on a set of columns in which all values must be unique.

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

Syntax

Visual Basic (Declaration)

Public Class UniqueConstraint _
    Inherits Constraint

Visual Basic (Usage)

Dim instance As UniqueConstraint

public class UniqueConstraint : Constraint

Visual C++

public ref class UniqueConstraint : public Constraint

JScript

public class UniqueConstraint extends Constraint

Remarks

The UniqueConstraint is enforced on a single column (or columns) to ensure that a primary key value is unique.

Constraints are not enforced unless the EnforceConstraints property is set to true.

When the a DataSet is merged with a second DataSet, constraints are not enforced until all merges are completed.

Examples

The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.

Visual Basic

Public Sub CreateDataTable()
    Dim dataTable As DataTable = New DataTable
    dataTable.Columns.Add("CustomerID", Type.GetType("System.String"))
    dataTable.Columns.Add("CompanyName", Type.GetType("System.String"))

    Dim uniqueConstraint As UniqueConstraint = _
      New UniqueConstraint("CustConstraint", _
      New DataColumn() {dataTable.Columns("CustomerID"), _
      dataTable.Columns("CompanyName")})

    dataTable.Constraints.Add(uniqueConstraint)
End Sub

Inheritance Hierarchy

System..::.Object
System.Data..::.Constraint
System.Data..::.UniqueConstraint

Thread Safety

This type is suitable for multithreaded read operations. You must synchronize any write operations.

Platforms

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.

Version Information