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Added comments in related instances descriptors.

This commit is contained in:
Aymeric Augustin 2015-09-19 22:50:57 +02:00
parent 497d915299
commit 2409a4241a
1 changed files with 23 additions and 6 deletions
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29
django/db/models/fields/related_descriptors.py
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@ -148,6 +148,9 @@ class ReverseSingleRelatedObjectDescriptor(object):
if instance is None:
return self
# The related instance is loaded from the database and then cached in
# the attribute defined in self.cache_name. It can also be pre-cached
# by the reverse accessor (SingleRelatedObjectDescriptor).
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
@ -159,6 +162,9 @@ class ReverseSingleRelatedObjectDescriptor(object):
qs = qs.filter(**self.field.get_reverse_related_filter(instance))
# Assuming the database enforces foreign keys, this won't fail.
rel_obj = qs.get()
# If this is a one-to-one relation, set the reverse accessor
# cache on the related object to the current instance to avoid
# an extra SQL query if it's accessed later on.
if not self.field.remote_field.multiple:
setattr(rel_obj, self.field.remote_field.get_cache_name(), instance)
setattr(instance, self.cache_name, rel_obj)
@ -232,10 +238,13 @@ class ReverseSingleRelatedObjectDescriptor(object):
for lh_field, rh_field in self.field.related_fields:
setattr(instance, lh_field.attname, getattr(value, rh_field.attname))
# Since we already know what the related object is, seed the related
# object caches now, too. This avoids another db hit if you get the
# object you just set.
# Set the related instance cache used by __get__ to avoid a SQL query
# when accessing the attribute we just set.
setattr(instance, self.cache_name, value)
# If this is a one-to-one relation, set the reverse accessor cache on
# the related object to the current instance to avoid an extra SQL
# query if it's accessed later on.
if value is not None and not self.field.remote_field.multiple:
setattr(value, self.field.remote_field.get_cache_name(), instance)
@ -312,6 +321,9 @@ class SingleRelatedObjectDescriptor(object):
if instance is None:
return self
# The related instance is loaded from the database and then cached in
# the attribute defined in self.cache_name. It can also be pre-cached
# by the forward accessor (ReverseSingleRelatedObjectDescriptor).
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
@ -325,6 +337,9 @@ class SingleRelatedObjectDescriptor(object):
except self.related.related_model.DoesNotExist:
rel_obj = None
else:
# Set the forward accessor cache on the related object to
# the current instance to avoid an extra SQL query if it's
# accessed later on.
setattr(rel_obj, self.related.field.get_cache_name(), instance)
setattr(instance, self.cache_name, rel_obj)
@ -386,10 +401,12 @@ class SingleRelatedObjectDescriptor(object):
for index, field in enumerate(self.related.field.local_related_fields):
setattr(value, field.attname, related_pk[index])
# Since we already know what the related object is, seed the related
# object caches now, too. This avoids another db hit if you get the
# object you just set.
# Set the related instance cache used by __get__ to avoid a SQL query
# when accessing the attribute we just set.
setattr(instance, self.cache_name, value)
# Set the forward accessor cache on the related object to the current
# instance to avoid an extra SQL query if it's accessed later on.
setattr(value, self.related.field.get_cache_name(), instance)