#29244: Passing dict to a Func subclass fails silently on hash step
----------------------------------------+------------------------
Reporter: Rob Jauquet | Owner: nobody
Type: Bug | Status: new
Component: Core (Other) | Version: 2.0
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 |
----------------------------------------+------------------------
With this code:
{{{#!python
from django.contrib.postgres.search import SearchQuery, Value, Func
from django.core.paginator import Paginator
from django.db.models import F, TextField, DateTimeField, Models
from django.utils import timezone
class Entry(Model):
text = TextField()
published_on = DateTimeField(default=timezone.now())
class Headline(Func):
function = 'ts_headline'
output_field = TextField()
def __init__(self, text, query, options=None):
extra = {}
expressions = [text, query]
if options:
opt_str = ''
for key, value in options.items():
opt_str += f'{key}={value},'
expressions.append(Value(opt_str[:-1]))
super().__init__(*expressions, **extra)
entries = Entry.objects.annotate(
text_highlighted=Headline(
F('text'),
SearchQuery('house'),
options={'HighlightAll': False},
)
).order_by('-published_on')
paginator = Paginator(entries, 20)
# evaluates the queryset
paginator.page(1)
}}}
Passing options by {{{dict}}} to the {{{Func}}} subclass causes the count
step for pagination to fail silently in paginator.py line 85 [#link1 (1)]
which is in turn caused by a silenced TypeError during the hash in
expressions.py line 372 [#link2 (2)].
Then, because of the fallback to {{{len}}} on paginator.py line 90 [#link3
(3)] the entire queryset is evaluated instead of evaluating just the
specified page (and in this specific case, calling ts_headline on every
row instead of just the first page).
The correct way of passing options using {{{**options}}} instead of
{{{options=None}}} fixes this case, but the silent error and fallback to
calling {{{len}}} on a queryset causes an unexpected expensive query when
using pagination.
[=#link1 (1)]
https://github.com/django/django/blob/master/django/core/paginator.py#L85
[=#link2 (2)]
https://github.com/django/django/blob/master/django/db/models/expressions.py#L372
[=#link3 (3)]
https://github.com/django/django/blob/master/django/core/paginator.py#L90
--
Ticket URL: <https://code.djangoproject.com/ticket/29244>
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