v0.3.2 breaks Django 1.8.4 about django-picklefield

[charettes]

Please provide a test case to reproduce.

[Koed00]

First think I found this morning is that v0.3.1 values_list('picklefield') would return undecoded strings. V0.3.2 decodes them. This breaks any code that tries to dbsafe_decode a values_list.

Running some more tests.

[Koed00]

The problem seems to be that in Django 1.8.4 , the values_list values are nice and decoded.
In Django 1.7.10 , the values_list values still return encoded .Which was the old behavior.

[Koed00]

testmodel = TestModel.objects.first()
testmodel.picklefield = 'hello'
TestModel.objects.filter(pk=testmodel.pk).values_list('picklefield', flat=True)[0]==testmodel.picklefield

In the current version , this is only true for Django 1.8.4 and not for Django 1.7.10
The fix for this used to be to dbsafe_decode the value, but since it's now already decoded with 1.8.4, dbsafe_decode raises an exception.

[charettes]

As of Django 1.8+ you should expect all fields to be automatically decoded when using values(_list)?() as documented in the release notes.

You weren't getting any failures when using django-picklefield==0.3.1 because it was using the deprecated SubfieldBase API that was removed in 9cabb40.

Since this Django change is definitely an improvement and is here to stay I'll close this ticket.

[Koed00]

Do you have a suggestion how I run my code on both versions of Django without having to resort to checking for Django versions?

[charettes]

I'm afraid this will really hard to achieve without relying on Django version checking. Can you point me to some code?

[Koed00]

I agree with you that this is a real improvement and I'm happy someone has taken it upon themselves to keep django-picklefield up to date.

    @staticmethod
    def get_result_group(group_id, failures=False):
        # values + decode is 10 times faster than just list comprehension
        if failures:
            values = Task.objects.filter(group=group_id).values_list('result', flat=True)
        else:
            values = Task.objects.filter(group=group_id).exclude(success=False).values_list('result', flat=True)
        return [dbsafe_decode(t) for t in values]

https://github.com/Koed00/django-q/blob/master/django_q/models.py

After the 0.3.2 update I removed the dbsafe_decode() iteration and that tested just fine. Unfortunately my projects tries to be 1.7 compatible too, so those tests then failed on Travis.
I've been thinking about refactoring a version of dbsafe_encode with a try clause in it, but that feels counterproductive. There is no real way of determining if a string is base64 encoded either.

[charettes]

I'd would suggest you create a compat module with the following code and import it wherever you need to do some conditional decoding.

from picklefield import PickledObjectField, dbsafe_decode

if hasattr(PickledObjectField, 'from_db_value'):
    def decode_results(values):
        return values
else:
    def decode_results(values):
        return [dbsafe_decode(v) for v in values]

[Koed00]

Perfect, thanks a million.

[charettes]

You could then replace your method by:

from .compat import decode_results
...
def get_result_group(group_id, failures=False):
    # values + decode is 10 times faster than just list comprehension
    if failures:
        values = Task.objects.filter(group=group_id).values_list('result', flat=True)
    else:
        values = Task.objects.filter(group=group_id).exclude(success=False).values_list('result', flat=True)
    return decode_results(values)

And simply remove the decode_results compatibly shim when dropping support for Django 1.7.