JSONField defaults to empty list gets modified

[Ponytech]

Consider this simple model :

from django.db import models
from django.contrib.postgres.fields import JSONField


class Thing(models.Model):
	name = models.CharField(max_length=100)
	features = JSONField(default=[], blank=True)

And this code snippet :

>>> t1 = Thing.objects.create(name="thing 1")
>>> t1.features.append({"f1": 42, "f2": 56})
>>> t1.features
[{'f1': 42, 'f2': 56}]
>>> t1.save()
>>> t2 = Thing.objects.create(name="thing 2")
>>> t2.features
[{'f1': 42, 'f2': 56}]

I'd expect t2 features to be an empty list.

My guess is the model default fields gets modified somehow.

[Jani Tiainen]

You've hit Python mutable default problem. Instead of defining mutable default [] use callable as default list in this particular case.

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