[Zope] Re: Zope Persistence (was: XML-RPC within ZOPE)

[Florent Guillaume]

Jan-Ole Esleben wrote:
>   security.declareProtected("Use TestPChanged", "test_internal")
>   def test_internal(self, args=None, args2=None):
>     "Called by test via XML-RPC"
>     if args2:
>         self.a.append(1)
>     self._p_changed = 1
>     if not args:
>         import xmlrpclib
>         s = xmlrpclib.ServerProxy("http://USER:PASSWORD@localhost:8080/",
>             allow_none=True)
>         s.TestPChanged.test_internal(1)
>     return self.a
> 
>   security.declareProtected("Use TestPChanged", "test")
>   def test(self, args2=None):
>     "Called directly via ZOPE"
>     if args2:
>         self.a.append(1)
>     self._p_changed = 1
>     import xmlrpclib
>     s = xmlrpclib.ServerProxy("http://USER:PASSWORD@localhost:8080/",
>         allow_none=True)
>     return s.TPCDest.test_internal()
> 
> 
> 1. In the example, just setting _p_changed=1 does _not_ lead to a
> conflict error. With the ineffectual code above it (that never gets
> executed) it _does_. So there _is_ some implicit magical stuff going
> on and ZOPE tries to take care that only subobjects change (but
> incompletely)!

I strongly doubt it. Zope does not "inspect code". There must be a 
problem in your testing. Note that if self.a is a standard list, the 
self.a.append(1) doesn't have any impact on the persistence mechanism or 
transactions either.

> 2. You shouldn't use lists and dicts - it should say this "on the
> front page". It is never really mentioned in any way that intuitively
> leads to such problems as we are now talking about. It isn't very
> obvious that things work like this when you look at the documentation,
> and

You should understand the persistence mechanism of a framework before 
using it. Zope's is simple to understand in the case where you work with 
a single transaction. Here you have a remote server that does a callback 
to the local and thus starts a new transaction parallel to the current 
one. In addition it touches the same object. Frankly that's a bizarre 
use case, nothing is "simple" about it.

> 3. It is especially confusing that ZOPE behaves differently when using
> XML-RPC calls. From what you say, it should be the same within the
> ZOPE system as when using XML-RPC. It gets more complicated with
> XML-RPC though!

The successive XML-RPC call you describe provoke new transactions, 
surely you're aware of that? Whereas just calling a function of course 
doesn't.

Florent

-- 
Florent Guillaume, Nuxeo (Paris, France)   Director of R&D
+33 1 40 33 71 59   http://nuxeo.com   fg at nuxeo.com