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django/django/contrib/contenttypes/prefetch.py at main · django/django · GitHub

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from django.db.models import Prefetch

from django.db.models.query import ModelIterable, RawQuerySet

class GenericPrefetch(Prefetch):

def __init__(self, lookup, querysets, to_attr=None):

for queryset in querysets:

if queryset is not None and (

isinstance(queryset, RawQuerySet)

or (

hasattr(queryset, "_iterable_class")

and not issubclass(queryset._iterable_class, ModelIterable)

)

raise ValueError(

"Prefetch querysets cannot use raw(), values(), and values_list()."

)

self.querysets = querysets

super().__init__(lookup, to_attr=to_attr)

def __getstate__(self):

obj_dict = self.__dict__.copy()

obj_dict["querysets"] = []

for queryset in self.querysets:

if queryset is not None:

queryset = queryset._chain()

# Prevent the QuerySet from being evaluated

queryset._result_cache = []

queryset._prefetch_done = True

obj_dict["querysets"].append(queryset)

return obj_dict

def get_current_querysets(self, level):

if self.get_current_prefetch_to(level) == self.prefetch_to:

return self.querysets

return None

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