Hi all,
On Sun, 12 May 2013, Shai Berger wrote:
those should probably be updated (on remote objects!) too, or else
some serious inconsistencies may be created (when the _id field
changes, that is).
aa= A.objects.get(...)
bb= aa.b
(some other operation, changing aa.b_id in the database)
aa.refresh()
Now -- unless we do something about it -- bb.a is still aa, but aa.b is not bb
and not even equal to it; thus, "bb.a.b == bb" is false, which currently
cannot happen without serious meddling if I'm not mistaken.
Hibernate (as an implementation of the Java Persistence API, JPA) tries to
do things like this by implementing a global cache of objects loaded from
the database, so that there's only one copy of A and B in memory, which
all references point to.
This makes it possible for A, when its link to B changes to point to a
different object B', to find all the instances of B in memory (because
there's only one, and it's in the object cache) and update them to no
longer point back to A.
However it does this at enormous cost in flexibility, sanity and error
recovery. I strongly recommend against going down this route:
http://blog.old.aptivate.org/2010/11/26/hibernate-ejb-and-the-unique-constraint/
It's always possible to have an out-of-date model object in memory with
Django, with or without refresh() (which just allows us to update it
manually). I suggest we let that sleeping dog lie.
Cheers, Chris.
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