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Fixed #17014 - added protection against infinite recursion. 

Thanks to akaariai for the report and tests.

No tests have been added, since unittests for termination are basically
impossible, and the failure condition will take down the developer's machine
in this case. It has been tested against the cases in #17014.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16940 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Luke Plant 2011-10-07 16:06:02 +00:00
parent 052a011ee6
commit 64da8eec30
1 changed files with 21 additions and 9 deletions
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30
django/db/models/query.py
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@ -3,6 +3,7 @@ The main QuerySet implementation. This provides the public API for the ORM.
"""
import copy
import itertools
from django.db import connections, router, transaction, IntegrityError
from django.db.models.fields import AutoField
@ -1574,9 +1575,12 @@ def prefetch_related_objects(result_cache, related_lookups):
# ensure we don't do duplicate work.
done_lookups = set() # list of lookups like foo__bar__baz
done_queries = {} # dictionary of things like 'foo__bar': [results]
related_lookups = list(related_lookups)
# We may expand related_lookups, so need a loop that allows for that
manual_lookups = list(related_lookups)
auto_lookups = [] # we add to this as we go through.
followed_descriptors = set() # recursion protection
related_lookups = itertools.chain(manual_lookups, auto_lookups)
for lookup in related_lookups:
if lookup in done_lookups:
# We've done exactly this already, skip the whole thing
@ -1616,7 +1620,7 @@ def prefetch_related_objects(result_cache, related_lookups):
# We assume that objects retrieved are homogenous (which is the premise
# of prefetch_related), so what applies to first object applies to all.
first_obj = obj_list[0]
prefetcher, attr_found, is_fetched = get_prefetcher(first_obj, attr)
prefetcher, descriptor, attr_found, is_fetched = get_prefetcher(first_obj, attr)
if not attr_found:
raise AttributeError("Cannot find '%s' on %s object, '%s' is an invalid "
@ -1638,10 +1642,17 @@ def prefetch_related_objects(result_cache, related_lookups):
obj_list = done_queries[current_lookup]
else:
obj_list, additional_prl = prefetch_one_level(obj_list, prefetcher, attr)
for f in additional_prl:
new_prl = LOOKUP_SEP.join([current_lookup, f])
related_lookups.append(new_prl)
done_queries[current_lookup] = obj_list
# We need to ensure we don't keep adding lookups from the
# same relationships to stop infinite recursion. So, if we
# are already on an automatically added lookup, don't add
# the new lookups from relationships we've seen already.
if not (lookup in auto_lookups and
descriptor in followed_descriptors):
for f in additional_prl:
new_prl = LOOKUP_SEP.join([current_lookup, f])
auto_lookups.append(new_prl)
done_queries[current_lookup] = obj_list
followed_descriptors.add(descriptor)
else:
# Either a singly related object that has already been fetched
# (e.g. via select_related), or hopefully some other property
@ -1659,8 +1670,9 @@ def get_prefetcher(instance, attr):
"""
For the attribute 'attr' on the given instance, finds
an object that has a get_prefetch_query_set().
Return a 3 tuple containing:
Returns a 4 tuple containing:
(the object with get_prefetch_query_set (or None),
the descriptor object representing this relationship (or None),
a boolean that is False if the attribute was not found at all,
a boolean that is True if the attribute has already been fetched)
"""
@ -1694,7 +1706,7 @@ def get_prefetcher(instance, attr):
rel_obj = getattr(instance, attr)
if hasattr(rel_obj, 'get_prefetch_query_set'):
prefetcher = rel_obj
return prefetcher, attr_found, is_fetched
return prefetcher, rel_obj_descriptor, attr_found, is_fetched
def prefetch_one_level(instances, prefetcher, attname):