AssertionError on identical chained queries

[emperorcezar]

The complier throws an error when there are two chained identical filters. The case that brought me to find this was when I creating a form for the admin.

I have the following line of code:

self.fields['faculty'].queryset = User.objects.filter(pk__in = [faculty.user.pk for faculty in faculty_list])

In the case where there is only one faculty user, and I create the object (in the admin form) selecting that one user, I will get an error triggered by the following line of django_mongodb_engine/compiler.py on line 245:

assert all(key not in existing for key in lookup.keys()), [lookup, existing]

What is causing this case to occur is the following code in the clean() method of Django's ModelChoiceField

qs = self.queryset.filter(**{'%s__in' % key: value})

where the value is the choice I selected.

Puting both of these together you get the query

User.objects.filter(pk__in = [u'4eaef5d7bb6933592e000010']).filter(pk__in = [u'4eaef5d7bb6933592e000010'])

and then the AssertionError triggers.

I'm trying to work on a patch right now, but I'm not real familiar with the complier. Any advice appreciated.

[jonashaag]

The only advice I can give is "good luck". The query generator is an unmaintainable mess and needs to be rewritten from scratch. Unfortunately I couldn't find the time to do it yet :-(

[emperorcezar]

Do you know the purpose of that assertion? I would like to code an exception there. The comments make it out that it's there in the case of a $gt and $lt query. If that's the case I can check if the query is $in and ignore the assertion.

[emperorcezar]

I'm going to try

else:
     # {'$o1} + {'$lt': o2} --> {'$gt': o1, '$lt': o2}
     if '$gt' in lookup or '$lt' in lookup:
         assert all(key not in existing for key in lookup.keys()), [lookup, existing]
     existing.update(lookup)

Is there a test suite for the driver?

[jonashaag]

It's to avoid overwriting what's been generated previously. Maybe you can special-case $in.

if lookup is an '$in' lookup and an '$in' lookup already exists:
    existing['$in'].extend(lookup['$in'])
else:
    go the normal way, including the exception

edit: you can put regression tests into tests/mongodb/tests.py.

[jonashaag]

Adam, any news on this issue?

[emperorcezar]

Sorry, had to jump off the project to do some quick fixes on another. The code I put up as trying seems to work fine. I haven't had a chance to do the more explicit exception you have laid out yet. I will make sure to do that soon and update my commit.