id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
14075	ManyToMany relationships create circular references	Andrea Corbellini	nobody	"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."		closed	Database layer (models, ORM)	1.2		wontfix		Andrea Corbellini	Unreviewed	0	0	0	0	0	0