Added comments in related instances descriptors. (2409a424) · Commits · Dom Sekotill / django

django/db/models/fields/related_descriptors.py

+23 −6

Original line number	Diff line number	Diff line
		@@ -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)