private void SetChildKeyConstraint ( DataSet ds ) {
   DataColumn cCol, pCol;
   // set child and parent columns.
   pCol = ds.Tables [ "Suppliers" ].Columns [ "SupplierID" ];
   cCol = ds.Tables [ "Products" ].Columns [ "SupplierID" ];
   DataRelation dr = new DataRelation ( "SuppliersConstraint", pCol, cCol )

   ForeignKeyConstraint fk = dr.ChildKeyConstraint;
   fk.DeleteRule = Rule.SetNull;
   fk.UpdateRule = Rule.Cascade;
   fk.AcceptRejectRule = AcceptRejectRule.Cascade;
}

Private Sub SetChildKeyConstraint ( ds As DataSet )
   Dim cCol, pCol As DataColumn
   ' set child and parent columns.
   pCol = ds.Tables ( "Suppliers" ).Columns ( "SupplierID" )
   cCol = ds.Tables ( "Products" ).Columns ( "SupplierID" )
   Dim dr As New DataRelation ( "SuppliersConstraint", pCol, cCol )

   Dim fk As ForeignKeyConstraint = dr.ChildKeyConstraint
   fk.DeleteRule = Rule.SetNull
   fk.UpdateRule = Rule.Cascade
   fk.AcceptRejectRule = AcceptRejectRule.Cascade
End Sub