[Twisted-Python] can pb.Copyable objects be compared for equality after a round trip?

[Robert Gravina]

> Only thing I can think of is generate your own id. Doesn't have to  
> be random, you can simply increament a counter every time you  
> create a new instance. If you're worried about the id growing too  
> long you can search the database for unused ids that are lower than  
> the current value of the counter.
>

While I appreciate your suggestions, given that PB is really quite  
powerful and pb.Referenceables can be identified after a round trip,  
I figure there must be a better way of doing this. I don't want to  
use pb.Referenceables because I need to access the objects attributes  
and call methods on the remote end. I'm not 100% sure that your  
method is bug-free, although I haven't had a good think about it.  
Thanks anyhow.

> Perhaps somebody else has a better idea.
>

I really hope so. I'm stuck for ideas, short of turning everything  
into pb.Cacheables.

Robert

> On 24/06/06, Robert Gravina <robert at gravina.com> wrote: This is an  
> old thread, but I am finally tackling the round trip
> editing problem and unfortunately getting nowhere. Basically, I want
> to be able to create some object on one machine, then send it off to
> another (who edits some of the attributes) then when the other
> machine calls a method on the original machine and passes it the
> updated object, I can identify it simply by comparing for quality.
> Think of your basic client/server database application.
>
> The Twisted howtos make the claim that " Copyable objects return
> unchanged from a round trip", and can be compared for quality like
> (obj == obj) but in all my attempts I can get this to work (they are
> never equal). Does someone know of some sample code where this is
> done successfully? It is done successfully with pb.Referenceables in
> the howtos (look for the pb2client.py and pb2server.py listings).
> http://twistedmatrix.com/projects/core/documentation/howto/pb- 
> usage.html
>
> Since I'm using the ZODB, I've tried using ZODB's _p_oid attribute to
> identify objects that come back to me but the _p_oid is  None even
> after a transaction.commit() (since the object hasn't been persisted
> yet probably).
>
> I could also create my own ID attribute and attempt to generate a
> random ID and compare that, but this is most definately a hack.
>
> I am really having trouble progressing with my application because of
> this problem. I'd really appreciate some insight on how to go about
> solving this. Admittedly I'm not all that experienced with Twisted,
> but I thought this kind of thing was supposed to be straightforward.
> What am I doing wrong?
>
> Thanks,
>
> Robert
>
> On 2006/05/07, at 18:55, Micky Latowicki wrote:
>
> > It's possible to make each element in the set being edited a
> > cacheable. If you think that would introduce too much overhead, then
> > you can add a method to the "address book" object which updates  
> one of
> > the entries in this address book, and uses an id to identify the  
> entry
> > within the address book. So the address book is the dict. That's  
> what
> > I did in a similar case. I'm no expert though.
> >
> > HTH
> >
> > Micky
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