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

For a list of all members of this type, see UniqueConstraint Members.

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

[Visual Basic]
<Serializable>
Public Class UniqueConstraint
   Inherits Constraint
[C#]
[Serializable]
public class UniqueConstraint : Constraint
[C++]
[Serializable]
public __gc class UniqueConstraint : public Constraint
[JScript]
public
   Serializable
class UniqueConstraint extends Constraint

Thread Safety

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

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.

Example

[Visual Basic] The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.

[Visual Basic] 
Public Sub CreateTable()
  Dim myTable As DataTable = New DataTable
  myTable.Columns.Add("CustomerID", Type.GetType("System.String"))
  myTable.Columns.Add("CompanyName", Type.GetType("System.String"))

  Dim myUC As UniqueConstraint = New UniqueConstraint("CustConstraint", _
                                     New DataColumn() {myTable.Columns("CustomerID"), _
                                                       myTable.Columns("CompanyName")} )
  myTable.Constraints.Add(myUC)
End Sub

[C#, C++, JScript] No example is available for C#, C++, or JScript. To view a Visual Basic example, click the Language Filter button in the upper-left corner of the page.

Requirements

Namespace: System.Data

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework - Windows CE .NET

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

See Also

UniqueConstraint Members | System.Data Namespace | Add | Constraint | Constraints | ConstraintCollection | DataRelation | ForeignKeyConstraint