#28312: ModelChoiceIterator uses cached length of queryset.
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Reporter: Sjoerd Job Postmus | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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In Django 1.8 (but also master), `ModelChoiceIterator` has the following
implementation:
{{{
class ModelChoiceIterator:
def __init__(self, field):
self.field = field
self.queryset = field.queryset
def __iter__(self):
if self.field.empty_label is not None:
yield ("", self.field.empty_label)
queryset = self.queryset.all()
# Can't use iterator() when queryset uses prefetch_related()
if not queryset._prefetch_related_lookups:
queryset = queryset.iterator()
for obj in queryset:
yield self.choice(obj)
def __len__(self):
return (len(self.queryset) + (1 if self.field.empty_label is not
None else 0))
def choice(self, obj):
return (self.field.prepare_value(obj),
self.field.label_from_instance(obj))
}}}
As can be seen, `__iter__` actually does a `.all()` to make sure it gets
fresh results. However, `__len__` does not. Also: it currently caches all
objects inside `self.queryset`, only releasing them again on shutdown
which might be problematic if there are a lot of results (or even a few
"large" results).
Suggested implementation
{{{
def __len__(self):
return self.queryset.count() + (1 if self.field.empty_label is not
None else 0))
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/28312>
Django <https://code.djangoproject.com/>
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