private void SetPrimaryKeys ( ) {
   // create a new DataTable and set two DataColumn objects as primary keys.
   DataTable myTable = new DataTable ( );
   DataColumn [ ] keys = new DataColumn [ 2 ];
   DataColumn myColumn;
   // create column 1.
   myColumn = new DataColumn ( );
   myColumn.DataType = System.Type.GetType ( "System.String" );
   myColumn.ColumnName = "FirstName";
   // add the column to the DataTable.Columns collection.
   myTable.Columns.Add ( myColumn );
   // add the column to the array.
   keys [ 0 ] = myColumn;

   // create column 2 and add it to the array.
   myColumn = new DataColumn ( );
   myColumn.DataType = System.Type.GetType ( "System.String" );
   myColumn.ColumnName = "LastName";
   myTable.Columns.Add ( myColumn );
   // add the column to the array.
   keys [ 1 ] = myColumn;
   // set the PrimaryKeys property to the array.
   myTable.PrimaryKey = keys;
}

Private Sub SetPrimaryKeys ( )
   ' create a new DataTable and set two DataColumn objects as primary keys.
   Dim myTable As DataTable = new DataTable ( )
   Dim keys ( 2 ) As DataColumn
   Dim myColumn  As DataColumn
   ' create column 1.
   myColumn = New DataColumn ( )
   myColumn.DataType = System.Type.GetType ( "System.String" )
   myColumn.ColumnName = "FirstName"
   ' add the column to the DataTable.Columns collection.
   myTable.Columns.Add ( myColumn )
   ' add the column to the array.
   keys ( 0 ) = myColumn

   ' create column 2 and add it to the array.
   myColumn = New DataColumn ( )
   myColumn.DataType = System.Type.GetType ( "System.String" )
   myColumn.ColumnName = "LastName"
   myTable.Columns.Add ( myColumn )
   ' add the column to the array.
   keys ( 1 ) = myColumn
   ' set the PrimaryKeys property to the array.
   myTable.PrimaryKey = keys
End Sub

Private void GetPrimaryKeys ( DataTable myTable ) {
   // create the array for the columns.
   DataColumn [ ] colKeys = myTable.PrimaryKey;
   // get the number of elements in the array.
   Response.Write ( "Column Count: " + colKeys.Length );

   for ( int i = 0; i < colKeys.Length; i++ ) {
      Response.Write ( colKeys [ ].ColumnName + 
         colKeys [ ].DataType );
   }
}

Private Sub GetPrimaryKeys ( myTable As DataTable )
   ' create the array for the columns.
   Dim colKeys ( ) As DataColumn = myTable.PrimaryKey
   ' get the number of elements in the array.
   Response.Write ( "Column Count: " & colKeys.Length.ToString ( ) )
   Dim i As Integer
   For i = 0 To colKeys.GetUpperBound ( 0 )
      Response.Write ( colKeys ( i ).ColumnName & _
         colKeys ( i ).DataType.ToString ( ) )
   Next i
End Sub