#14075: ManyToMany relationships create circular references
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Reporter: candrea | Owner: nobody
Status: new | Milestone:
Component: Uncategorized | Version: 1.2
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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Here is how you can reproduce the problem:
1. First, download the attached tar.gz which contains a simple Django
project with an app. The important file is models.py, that contains the
m2m relationship.
2. Open a Python console and enable DEBUG_SAVEALL in the GC:
{{{
>>> import gc
>>> gc.set_debug(gc.DEBUG_SAVEALL)
}}}
3. Import the 'models' module from the Django app:
{{{
>>> from testproj.testapp import models
}}}
4. Run a full collection and check the garbage:
{{{
>>> gc.collect()
6
>>> gc.garbage
[..., <class 'django.db.models.fields.related.Meta'>, ...]
}}}
In most of the cases this isn't a problem, because the GC without
DEBUG_SAVEALL automatically deletes such objects. However this becomes an
issue when you want to disable the garbage collector to increase
performances a bit. This problem is caused by the fact that creating a
Python's new-style class creates circular references and in fact 'Meta' is
a new-style class.
I see that this problem occurs for almost every operation that involves a
many-to-many relationships: the Meta class is created (sometimes more than
one time) and then is deleted. To avoid the problem, I think that Meta
shouldn't be a temporary class, but should be saved somewhere in the
model, so that it will never be deleted till the interpreter exits (or the
model is destroyed). Using a dictionary instead of a class may solve the
problem too.
--
Ticket URL: <http://code.djangoproject.com/ticket/14075>
Django <http://code.djangoproject.com/>
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