private void DemonstrateEnforceConstraints ( ) {
   // create a DataSet with one table, one column and a UniqueConstraint.
   DataSet ds = new DataSet ( "myDataSet" );
   DataTable t = new DataTable ( "myTable" );
   DataColumn c = new DataColumn ( "col1" );
   // a UniqueConstraint is added when the Unique property is true.
   c.Unique = true;
   t.Columns.Add ( c );
   ds.Tables.Add ( t );
   Response.Write ( "constraints.count: " + t.Constraints.Count );
   // add five rows.
   DataRow r ;
   for ( int i=0; i < 5; i++ ) {
      r = t.NewRow ( );
      r [ "col1" ] = i;
      t.Rows.Add ( r );
  }
   t.AcceptChanges ( );

   ds.EnforceConstraints = false;
   // change the values of all rows to 1.
   foreach ( DataRow thisRow in t.Rows ) {
      thisRow [ "col1" ] = 1;
      // Response.Write ( "<br>" + thisRow [ 0 ] );
  }
   try {
      ds.EnforceConstraints = true;
  }
   catch ( System.Data.ConstraintException ex ) {
      Response.Write ( "ConstraintException: " + ex.Message );
  }
   catch ( System.Exception sysEx ) {
      Response.Write ( sysEx.GetType ( ).Name );
      Response.Write ( sysEx.Message );
   }
}

Private Sub DemonstrateEnforceConstraints ( )
   ' create a DataSet with one table, one column and a UniqueConstraint.
   Dim ds As DataSet = New DataSet ( "myDataSet" )
   Dim t As DataTable = New DataTable ( "myTable" )
   Dim c As DataColumn = New DataColumn ( "col1" )
   c.Unique = True
   t.Columns.Add ( c )
   ds.Tables.Add ( t )
   Response.Write ( "constraints.count: " & t.Constraints.Count )
   ' add five rows.
   Dim r As DataRow
   Dim i As Integer
   For i = 0 To 4
      r = t.NewRow ( )
      r ( "col1" ) = i
      t.Rows.Add ( r )
   Next
   t.AcceptChanges ( )

   ds.EnforceConstraints = False
   ' change the values of all rows to 1.
   Dim thisRow As DataRow
   For Each thisRow In t.rows
      thisRow ( "col1" ) = 1
   Next
   Try
       ds.EnforceConstraints = True

   Catch ex As System.Data.ConstraintException
       Response.Write ( "ConstraintException: " + ex.Message )

   catch sysEx As System.Exception
      Response.Write ( sysEx.GetType ( ).Name );
      Response.Write ( sysEx.Message );
   End Try
End Sub