#26600: map says a queryset is not iterable
-------------------------------------+-------------------------------------
Reporter: ihucos | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution: wontfix
Keywords: queryset iterator | Triage Stage:
map | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Abhijeet):
I'm unsure if bumping this up is against forum rules. However, I get this
Error in Py3k in production. I'm not using `map` in my code, though I'm
unsure if Django is internally using it.
This is the code block that produces the error. The save method is
overriding the save method of a Mode called `Transaction`.
{{{
def save(self, *args, **kwargs):
obj = self
if not obj.ref_number: # Set the reference number before saving
transactions = Transaction.objects.values_list("ref_number",
flat=True) # cache the list
while True:
ref_number = random.randint(1000000001, 9999999999)
if ref_number not in transactions:
obj.ref_number = ref_number
super(Transaction, obj).save(*args, **kwargs)
return
else:
super(Transaction, obj).save(*args, **kwargs)
}}}
The erroring line of code is: `if ref_number not in transactions:`
This piece of code was working fine until we had modified another
unrelated part of the source code.
{{{
items =
OrderItem.objects.prefetch_related('toppings').select_related('item').select_related('item__category')
order = Order.objects.filter(uuid=order_uuid).prefetch_related(
Prefetch(
lookup='items',
queryset=items
)
).select_related('outlet').select_related('user').select_related('outlet__group')
\
.select_for_update(of=('self', 'outlet'))
}}}
What we did was add the call to `select_for_update`, followed by a
transaction which modifies the `Order` and `Outlet` model. Here, the
`Order` model is a child model of the `Transaction` model.
My guess as to what the problem is is that `select_for_update` locks the
relevant rows/table which results in the line of code in the `save` method
to fail internally, ultimately being caught as a cryptic type error. I'll
be modifying
`transactions = Transaction.objects.values_list("ref_number", flat=True)`
to
`transactions = Transaction.objects.values_list("ref_number",
flat=True).list()` to see if that'll fix the problem.
PS: I'm sorry if my formatting/post/bump is against norms. I'm new here,
with this being my first comment.
Replying to [comment:8 Simon Charette]:
> I think we can close as ''wontfix'' given `map` doesn't turn
`__iter__()` exceptions into `TypeError` on Py3k and we don't support Py2k
anymore.
>
> Thanks for the investigation Vitaliy.
--
Ticket URL: <https://code.djangoproject.com/ticket/26600#comment:13>
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