private void SetConstraint ( DataSet myDataSet, string table1, 
      string table2, string column1, string column2 ) {

   // declare parent column and child column variables.
   DataColumn parentColumn;
   DataColumn childColumn;
   ForeignKeyConstraint myFKeyConst;

   // set parent and child column variables.
   parentColumn = myDataSet.Tables [ Table1 ].Columns [ Column1 ];
   childColumn = myDataSet.Tables [ Table2 ].Columns [ Column2 ];
   myFKeyConst = new ForeignKeyConstraint
      ( "SupplierFKeyConst",  parentColumn, childColumn );

   // set null values when a value is deleted.
   myFKeyConst.DeleteRule = Rule.SetNull;
   myFKeyConst.UpdateRule = Rule.Cascade;
   myFKeyConst.AcceptRejectRule = AcceptRejectRule.Cascade;

   // add the constraint, and set EnforceConstraints to true.
   myDataSet.Tables [ Table1 ].Constraints.Add ( myFKeyConst );
   myDataSet.EnforceConstraints = true;
}

Private Sub SetConstraint ( myDataSet As DataSet, table1 As String, _
      table2 As String, column1 As String, column2 As String )

   ' declare parent column and child column variables.
   Dim parentColumn As DataColumn
   Dim childColumn As DataColumn
   Dim myFKeyConst As ForeignKeyConstraint

   ' set parent and child column variables.
   parentColumn = myDataSet.Tables ( table1 ).Columns ( column1 )
   childColumn = myDataSet.Tables ( table2 ).Columns ( column2 )
   myFKeyConst = New ForeignKeyConstraint _
      ( "SupplierFKeyConst", parentColumn, childColumn )

   ' set null values when a value is deleted.
   myFKeyConst.DeleteRule = Rule.SetNull
   myFKeyConst.UpdateRule = Rule.Cascade
   myFKeyConst.AcceptRejectRule = AcceptRejectRule.Cascade

   ' add the constraint, and set EnforceConstraints to true.
   myDataSet.Tables ( table1 ).Constraints.Add ( myFKeyConst )
   myDataSet.EnforceConstraints = True
End Sub