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[1.7.x] Refs #25693 -- Avoided redundant calls to get_fields() in to_attr validation.

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Conflicts:
	django/db/models/query.py

Backport of cc8c02fa0fa2119704d1c39ca8509850aef84acc from master
This commit is contained in:
Simon Charette 2015-11-11 00:40:20 -05:00
parent 6184cb9baa
commit 3d037b9f68
1 changed files with 11 additions and 8 deletions
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19
django/db/models/query.py
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@ -1906,17 +1906,20 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
rel_attr_val = rel_obj_attr(rel_obj)
rel_obj_cache.setdefault(rel_attr_val, []).append(rel_obj)
to_attr, as_attr = lookup.get_current_to_attr(level)
# Make sure `to_attr` does not conflict with a field.
if as_attr and instances:
# We assume that objects retrieved are homogeneous (which is the premise
# of prefetch_related), so what applies to first object applies to all.
model = instances[0].__class__
for related_m2m in model._meta.get_all_related_many_to_many_objects():
if related_m2m.get_accessor_name() == to_attr:
msg = 'to_attr={} conflicts with a field on the {} model.'
raise ValueError(msg.format(to_attr, model.__name__))
for obj in instances:
instance_attr_val = instance_attr(obj)
vals = rel_obj_cache.get(instance_attr_val, [])
to_attr, as_attr = lookup.get_current_to_attr(level)
# Check we are not shadowing a field on obj.
if as_attr:
for related_m2m in obj._meta.get_all_related_many_to_many_objects():
if related_m2m.get_accessor_name() == to_attr:
msg = 'to_attr={} conflicts with a field on the {} model.'
raise ValueError(msg.format(to_attr, obj.__class__.__name__))
if single:
val = vals[0] if vals else None