🚀 go-pugleaf

abulka@my-deja.com wrote:
> Mark Fussell <mark.fussell@chimu.com> wrote:
> > actually you should be able to do the above with:
> >
> >     void removeOrder( Order order ) {
> >         order.setCustomer(null);
> >     }
> >
> > which would keep all the association-controlling logic in the
> > 'setCustomer' method.
> 
> I don't think this would work because the Order class / controlling
> side is not being told WHICH customer to no longer point to.  The hash
> set _orders that lives in Customer needs to be updated, somehow.
> 
> Which was exactly my point, the Customer side needs to be:
> 
>  void removeOrder( Order order ) {
>   _orders.remove( order )   // this line is inelegant, but needed.
>   order.setCustomer(null);  // this line is ok, calls controlling side
>  }

Please review the pattern's example code again or simply try out the
version I gave.  Order::setCustomer already contains the functionality
you are trying to put into 'removeOrder' -- it already knows how to
remove itself from its (only) customer's collection of orders.  Remember
that an Order can only have a single customer because of the cardinality
rules (Martin gave a different example for the many-to-many
implementation).  

I am not saying you can't do it multiple ways, but I would say the
simple:
   void removeOrder( Order order ) {
      order.setCustomer(null);
   }
works correctly and is probably in the spirit of what Martin was trying
to show.  

Now I would agree that you might want to enhance the above to do a
simple integrity check:

     /**
      *@require order.customer = self
      */
   void removeOrder( Order order ) {
      order.setCustomer(null);
   }

Since it is a bit peculiar to allow a customer to clear out an order
that wasn't for that customer.  You could also simply ignore a request
to remove an order that doesn't belong to this customer if you want to
be more tolerant.  

   void removeOrder( Order order ) {
      if (!_orders.contains(order)) return;
      order.setCustomer(null);
   }

But in either case, Order::setCustomer is still controlling the
association.

--Mark
mark.fussell@chimu.com