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import django
from django.db import (
DEFAULT_DB_ALIAS,
NotSupportedError,
connections,
)
from django.db.models import Q, Window
from django.db.models.fields import related_descriptors
from django.db.models.functions import RowNumber
from django.db.models.lookups import GreaterThan, LessThanOrEqual
from django.db.models.sql import Query
from django.db.models.sql.constants import INNER
from django.db.models.sql.where import AND
def apply_pagination_fix():
"""Apply pagination fix for Django 5.1 or older.
This is based on the fix in this patch, which is going to be included in Django 5.2:
https://code.djangoproject.com/ticket/35677#comment:9
If can safely be removed when Django 5.2 is the minimum version we support
"""
if django.VERSION >= (5, 2):
return
# This is a copy of the function, exactly as it exists on Django 4.2, 5.0 and 5.1
# (there are no differences in this function between these versions)
def _filter_prefetch_queryset(queryset, field_name, instances):
predicate = Q(**{f"{field_name}__in": instances})
db = queryset._db or DEFAULT_DB_ALIAS
if queryset.query.is_sliced:
if not connections[db].features.supports_over_clause:
raise NotSupportedError(
"Prefetching from a limited queryset is only supported on backends "
"that support window functions."
)
low_mark, high_mark = queryset.query.low_mark, queryset.query.high_mark
order_by = [
expr for expr, _ in queryset.query.get_compiler(using=db).get_order_by()
]
window = Window(RowNumber(), partition_by=field_name, order_by=order_by)
predicate &= GreaterThan(window, low_mark)
if high_mark is not None:
predicate &= LessThanOrEqual(window, high_mark)
queryset.query.clear_limits()
# >> ORIGINAL CODE
# return queryset.filter(predicate) # noqa: ERA001
# << ORIGINAL CODE
# >> PATCHED CODE
queryset.query.add_q(predicate, reuse_all_aliases=True)
return queryset
# << PATCHED CODE
related_descriptors._filter_prefetch_queryset = _filter_prefetch_queryset # type: ignore
# This is a copy of the function, exactly as it exists on Django 4.2, 5.0 and 5.1
# (there are no differences in this function between these versions)
def add_q(self, q_object, reuse_all_aliases=False):
existing_inner = {
a for a in self.alias_map if self.alias_map[a].join_type == INNER
}
# >> ORIGINAL CODE
# clause, _ = self._add_q(q_object, self.used_aliases) # noqa: ERA001
# << ORIGINAL CODE
# >> PATCHED CODE
if reuse_all_aliases: # noqa: SIM108
can_reuse = set(self.alias_map)
else:
can_reuse = self.used_aliases
clause, _ = self._add_q(q_object, can_reuse)
# << PATCHED CODE
if clause:
self.where.add(clause, AND)
self.demote_joins(existing_inner)
Query.add_q = add_q
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