Pickling QuerySet with related fields fails

[Dmitry Shevchenko]

Assume we have two related models:

from django.db import models

class Group(models.Model):
    title = models.CharField(max_length=10)
        
class Event(models.Model):
    group = models.ForeignKey('Group')

Pickling queryset with filtering by group then fails:

>>>pickle.dumps(Event.objects.filter(group=1))
PicklingError: Can't pickle <function _curried at 0x101fdd5f0>: it's not found as django.utils.functional._curried

However, if i specify that i'm filtering on __pk lookup, then it suddenly works:

pickle.dumps(Event.objects.filter(group__pk=1))

[Dmitry Shevchenko]

Ok found this evil function :)

In [61]: Event.objects.filter(group=1).query.where.children[0].children[0][0].field.related_query_name
Out[61]: <function _curried at 0x101fdd5f0>

[Alex Gaynor]

Initial version, seems to be working, fixes all teh tickets about pickling translatable strings as well.

[mrts]

Let me point out that there's an important difference in behaviour in of delayed loading in Alex's patch. Namely, as with Alex's, Malcolm's code installs the reference to delayed_loader() as a proxy for every real translation function. But when delayed_loader() runs, it substitutes the references to itself with the actual functions from the imported real translation module in Malcolm's version. So it will be called exactly once and function calls will be fast subsequently.

As of now, Alex's version retains the references so that all calls to translation functions actually pass through delayed_loader(). As

• calls to translation functions are frequent and
• imports inside a function make calling it rather slow compared with a simple proxy function call (which is somewhat unexpected -- one would assume that only the first call to import is expensive and others cheap once the module is loaded -- but only timeit will tell as they say :) )

I recommend retaining Malcolm's optimized version. Currying is fine though and makes the code more readable IMHO.

See discussion at ​http://botland.oebfare.com/logger/django-dev/2010/3/20/3/ .

[Alex Gaynor]

Added some forgotten files (tests), also updated some comments.

[Alex Gaynor]

Killed some, now dead, code.

[Russell Keith-Magee]

(In [12866]) Fixed #12769, #12924 -- Corrected the pickling of curried and lazy objects, which was preventing queries with translated or related fields from being pickled. And lo, Alex Gaynor didst slayeth the dragon.

[Jacob]

Milestone 1.2 deleted