This is forbidden when an 'atomic' block is active. Django 1.8

Question

I am receiving the error This is forbidden when an 'atomic' block is active. on a Django 1.8 install.

I've tried wrapping it in both with transaction.atomic(): as well as creating an exception for IntegrityError

Here's my code:

item = Item.objects.filter(item_id = data['item_id'])[:1][0]
iserializer = ItemSerializer(item, data=data, partial=True)
try:
    with transaction.atomic():
        if iserializer and iserializer.is_valid():
            iserializer.save()
except IntegrityError:
    pass

What could be causing it? Why is my exception handling not working to keep this error from being received?

Here's the traceback:

Traceback (most recent call last):
  File "<console>", line 4, in <module>
  File "/home/vagrant/client/venv/bin/local/lib/python2.7/site-packages/rest_framework/serializers.py", line 186, in save
    self.instance = self.update(self.instance, validated_data)
  File "/home/vagrant/client/venv/bin/local/lib/python2.7/site-packages/rest_framework/serializers.py", line 880, in update
    instance.save()
  File "/vagrant/client/client/items/models.py", line 45, in save
    transaction.commit()
  File "/home/vagrant/client/venv/bin/local/lib/python2.7/site-packages/django/db/transaction.py", line 42, in commit
    get_connection(using).commit()
  File "/home/vagrant/client/venv/bin/local/lib/python2.7/site-packages/django/db/backends/base/base.py", line 172, in commit
    self.validate_no_atomic_block()
  File "/home/vagrant/client/venv/bin/local/lib/python2.7/site-packages/django/db/backends/base/base.py", line 322, in validate_no_atomic_block
    "This is forbidden when an 'atomic' block is active.")
TransactionManagementError: This is forbidden when an 'atomic' block is active.

Answer 1

Based on the traceback, it looks like you're overriding the model's save() method and explicitly calling transaction.commit().

File "/vagrant/client/client/items/models.py", line 45, in save
  transaction.commit()

As the error indicates, you can't do that inside an atomic block since the block is expecting to do that itself.

More fundamentally, the error here is in mixing the high-level transactions API (transaction.atomic()) and the low-level transactions API (transaction.commit()). They are meant to be alternatives to each other, not used together.

From the documentation:

Always prefer atomic() if possible at all. It accounts for the idiosyncrasies of each database and prevents invalid operations. The low level APIs are only useful if you’re implementing your own transaction management.