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Refs #16043 -- Refactored internal fields value cache. 

* Removed all hardcoded logic for _{fieldname}_cache.
* Added an internal API for interacting with the field values cache.

Thanks carljm and MarkusH for support.
This commit is contained in:
Paulo 2016-06-04 16:10:37 -07:00 committed by Tim Graham
parent 22ff86ec52
commit bfb746f983
11 changed files with 156 additions and 107 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
django/contrib/contenttypes/fields.py
View File

@ -7,6 +7,7 @@ from django.core.exceptions import FieldDoesNotExist, ObjectDoesNotExist
from django.db import DEFAULT_DB_ALIAS, models, router, transaction
from django.db.models import DO_NOTHING
from django.db.models.base import ModelBase, make_foreign_order_accessors
from django.db.models.fields.mixins import FieldCacheMixin
from django.db.models.fields.related import (
ForeignObject, ForeignObjectRel, ReverseManyToOneDescriptor,
lazy_related_operation,
@ -15,7 +16,7 @@ from django.db.models.query_utils import PathInfo
from django.utils.functional import cached_property
class GenericForeignKey:
class GenericForeignKey(FieldCacheMixin):
"""
Provide a generic many-to-one relation through the ``content_type`` and
``object_id`` fields.
@ -49,7 +50,6 @@ class GenericForeignKey:
def contribute_to_class(self, cls, name, **kwargs):
self.name = name
self.model = cls
self.cache_attr = "_%s_cache" % name
cls._meta.add_field(self, private=True)
setattr(cls, name, self)
@ -156,6 +156,9 @@ class GenericForeignKey:
else:
return []
def get_cache_name(self):
return self.name
def get_content_type(self, obj=None, id=None, using=None):
if obj is not None:
return ContentType.objects.db_manager(obj._state.db).get_for_model(
@ -203,14 +206,14 @@ class GenericForeignKey:
return (model._meta.pk.get_prep_value(getattr(obj, self.fk_field)),
model)
return (ret_val,
return (
ret_val,
lambda obj: (obj.pk, obj.__class__),
gfk_key,
True,
self.name)
def is_cached(self, instance):
return hasattr(instance, self.cache_attr)
self.name,
True,
)
def __get__(self, instance, cls=None):
if instance is None:
@ -224,23 +227,19 @@ class GenericForeignKey:
ct_id = getattr(instance, f.get_attname(), None)
pk_val = getattr(instance, self.fk_field)
try:
rel_obj = getattr(instance, self.cache_attr)
except AttributeError:
rel_obj = None
else:
if rel_obj and (ct_id != self.get_content_type(obj=rel_obj, using=instance._state.db).id or
rel_obj._meta.pk.to_python(pk_val) != rel_obj.pk):
rel_obj = None
rel_obj = self.get_cached_value(instance, default=None)
if rel_obj is not None:
ct_match = ct_id == self.get_content_type(obj=rel_obj, using=instance._state.db).id
pk_match = rel_obj._meta.pk.to_python(pk_val) == rel_obj.pk
if ct_match and pk_match:
return rel_obj
else:
rel_obj = None
if ct_id is not None:
ct = self.get_content_type(id=ct_id, using=instance._state.db)
with suppress(ObjectDoesNotExist):
rel_obj = ct.get_object_for_this_type(pk=pk_val)
setattr(instance, self.cache_attr, rel_obj)
self.set_cached_value(instance, rel_obj)
return rel_obj
def __set__(self, instance, value):
@ -252,7 +251,7 @@ class GenericForeignKey:
setattr(instance, self.ct_field, ct)
setattr(instance, self.fk_field, fk)
setattr(instance, self.cache_attr, value)
self.set_cached_value(instance, value)
class GenericRel(ForeignObjectRel):
@ -534,11 +533,14 @@ def create_generic_related_manager(superclass, rel):
# We (possibly) need to convert object IDs to the type of the
# instances' PK in order to match up instances:
object_id_converter = instances[0]._meta.pk.to_python
return (queryset.filter(**query),
return (
queryset.filter(**query),
lambda relobj: object_id_converter(getattr(relobj, self.object_id_field_name)),
lambda obj: obj.pk,
False,
self.prefetch_cache_name)
self.prefetch_cache_name,
False,
)
def add(self, *objs, bulk=True):
db = router.db_for_write(self.model, instance=self.instance)

20
django/db/models/base.py
View File

@ -378,6 +378,7 @@ class ModelState:
# Necessary for correct validation of new instances of objects with explicit (non-auto) PKs.
# This impacts validation only; it has no effect on the actual save.
self.adding = True
self.fields_cache = {}
class Model(metaclass=ModelBase):
@ -607,12 +608,12 @@ class Model(metaclass=ModelBase):
continue
setattr(self, field.attname, getattr(db_instance, field.attname))
# Throw away stale foreign key references.
if field.is_relation and field.get_cache_name() in self.__dict__:
rel_instance = getattr(self, field.get_cache_name())
if field.is_relation and field.is_cached(self):
rel_instance = field.get_cached_value(self)
local_val = getattr(db_instance, field.attname)
related_val = None if rel_instance is None else getattr(rel_instance, field.target_field.attname)
if local_val != related_val or (local_val is None and related_val is None):
del self.__dict__[field.get_cache_name()]
field.delete_cached_value(self)
self._state.db = db_instance._state.db
def serializable_value(self, field_name):
@ -646,13 +647,9 @@ class Model(metaclass=ModelBase):
# a ForeignKey or OneToOneField on this model. If the field is
# nullable, allowing the save() would result in silent data loss.
for field in self._meta.concrete_fields:
if field.is_relation:
# If the related field isn't cached, then an instance hasn't
# been assigned and there's no need to worry about this check.
try:
getattr(self, field.get_cache_name())
except AttributeError:
continue
if field.is_relation and field.is_cached(self):
obj = getattr(self, field.name, None)
# A pk may have been assigned manually to a model instance not
# saved to the database (or auto-generated in a case like
@ -663,7 +660,7 @@ class Model(metaclass=ModelBase):
if obj and obj.pk is None:
# Remove the object from a related instance cache.
if not field.remote_field.multiple:
delattr(obj, field.remote_field.get_cache_name())
field.remote_field.delete_cached_value(obj)
raise ValueError(
"save() prohibited to prevent data loss due to "
"unsaved related object '%s'." % field.name
@ -773,9 +770,8 @@ class Model(metaclass=ModelBase):
# the related object cache, in case it's been accidentally
# populated. A fresh instance will be re-built from the
# database if necessary.
cache_name = field.get_cache_name()
if hasattr(self, cache_name):
delattr(self, cache_name)
if field.is_cached(self):
field.delete_cached_value(self)
def _save_table(self, raw=False, cls=None, force_insert=False,
force_update=False, using=None, update_fields=None):

3
django/db/models/fields/__init__.py
View File

@ -734,9 +734,6 @@ class Field(RegisterLookupMixin):
column = self.db_column or attname
return attname, column
def get_cache_name(self):
return '_%s_cache' % self.name
def get_internal_type(self):
return self.__class__.__name__

26
django/db/models/fields/mixins.py Normal file
View File

@ -0,0 +1,26 @@
NOT_PROVIDED = object()
class FieldCacheMixin:
"""Provide an API for working with the model's fields value cache."""
def get_cache_name(self):
raise NotImplementedError
def get_cached_value(self, instance, default=NOT_PROVIDED):
cache_name = self.get_cache_name()
try:
return instance._state.fields_cache[cache_name]
except KeyError:
if default is NOT_PROVIDED:
raise
return default
def is_cached(self, instance):
return self.get_cache_name() in instance._state.fields_cache
def set_cached_value(self, instance, value):
instance._state.fields_cache[self.get_cache_name()] = value
def delete_cached_value(self, instance):
del instance._state.fields_cache[self.get_cache_name()]

6
django/db/models/fields/related.py
View File

@ -16,6 +16,7 @@ from django.utils.functional import cached_property, curry
from django.utils.translation import gettext_lazy as _
from . import Field
from .mixins import FieldCacheMixin
from .related_descriptors import (
ForwardManyToOneDescriptor, ForwardOneToOneDescriptor,
ManyToManyDescriptor, ReverseManyToOneDescriptor,
@ -78,7 +79,7 @@ def lazy_related_operation(function, model, *related_models, **kwargs):
return apps.lazy_model_operation(partial(function, **kwargs), *model_keys)
class RelatedField(Field):
class RelatedField(FieldCacheMixin, Field):
"""Base class that all relational fields inherit from."""
# Field flags
@ -438,6 +439,9 @@ class RelatedField(Field):
"The relation has multiple target fields, but only single target field was asked for")
return target_fields[0]
def get_cache_name(self):
return self.name
class ForeignObject(RelatedField):
"""

80
django/db/models/fields/related_descriptors.py
View File

@ -86,7 +86,6 @@ class ForwardManyToOneDescriptor:
def __init__(self, field_with_rel):
self.field = field_with_rel
self.cache_name = self.field.get_cache_name()
@cached_property
def RelatedObjectDoesNotExist(self):
@ -100,7 +99,7 @@ class ForwardManyToOneDescriptor:
)
def is_cached(self, instance):
return hasattr(instance, self.cache_name)
return self.field.is_cached(instance)
def get_queryset(self, **hints):
return self.field.remote_field.model._base_manager.db_manager(hints=hints).all()
@ -114,6 +113,7 @@ class ForwardManyToOneDescriptor:
instance_attr = self.field.get_local_related_value
instances_dict = {instance_attr(inst): inst for inst in instances}
related_field = self.field.foreign_related_fields[0]
remote_field = self.field.remote_field
# FIXME: This will need to be revisited when we introduce support for
# composite fields. In the meantime we take this practical approach to
@ -121,7 +121,7 @@ class ForwardManyToOneDescriptor:
# (related_name ends with a '+'). Refs #21410.
# The check for len(...) == 1 is a special case that allows the query
# to be join-less and smaller. Refs #21760.
if self.field.remote_field.is_hidden() or len(self.field.foreign_related_fields) == 1:
if remote_field.is_hidden() or len(self.field.foreign_related_fields) == 1:
query = {'%s__in' % related_field.name: {instance_attr(inst)[0] for inst in instances}}
else:
query = {'%s__in' % self.field.related_query_name(): instances}
@ -129,12 +129,11 @@ class ForwardManyToOneDescriptor:
# Since we're going to assign directly in the cache,
# we must manage the reverse relation cache manually.
if not self.field.remote_field.multiple:
rel_obj_cache_name = self.field.remote_field.get_cache_name()
if not remote_field.multiple:
for rel_obj in queryset:
instance = instances_dict[rel_obj_attr(rel_obj)]
setattr(rel_obj, rel_obj_cache_name, instance)
return queryset, rel_obj_attr, instance_attr, True, self.cache_name
remote_field.set_cached_value(rel_obj, instance)
return queryset, rel_obj_attr, instance_attr, True, self.field.get_cache_name(), False
def get_object(self, instance):
qs = self.get_queryset(instance=instance)
@ -154,23 +153,24 @@ class ForwardManyToOneDescriptor:
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
# The related instance is loaded from the database and then cached
# by the field on the model instance state. It can also be pre-cached
# by the reverse accessor (ReverseOneToOneDescriptor).
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
rel_obj = self.field.get_cached_value(instance)
except KeyError:
val = self.field.get_local_related_value(instance)
if None in val:
rel_obj = None
else:
rel_obj = self.get_object(instance)
remote_field = self.field.remote_field
# 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)
if not remote_field.multiple:
remote_field.set_cached_value(rel_obj, instance)
self.field.set_cached_value(instance, rel_obj)
if rel_obj is None and not self.field.null:
raise self.RelatedObjectDoesNotExist(
@ -208,6 +208,7 @@ class ForwardManyToOneDescriptor:
if not router.allow_relation(value, instance):
raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)
remote_field = self.field.remote_field
# If we're setting the value of a OneToOneField to None, we need to clear
# out the cache on any old related object. Otherwise, deleting the
# previously-related object will also cause this object to be deleted,
@ -219,13 +220,13 @@ class ForwardManyToOneDescriptor:
# populated the cache, then we don't care - we're only accessing
# the object to invalidate the accessor cache, so there's no
# need to populate the cache just to expire it again.
related = getattr(instance, self.cache_name, None)
related = self.field.get_cached_value(instance, default=None)
# If we've got an old related object, we need to clear out its
# cache. This cache also might not exist if the related object
# hasn't been accessed yet.
if related is not None:
setattr(related, self.field.remote_field.get_cache_name(), None)
remote_field.set_cached_value(related, None)
for lh_field, rh_field in self.field.related_fields:
setattr(instance, lh_field.attname, None)
@ -237,13 +238,13 @@ class ForwardManyToOneDescriptor:
# Set the related instance cache used by __get__ to avoid an SQL query
# when accessing the attribute we just set.
setattr(instance, self.cache_name, value)
self.field.set_cached_value(instance, 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)
if value is not None and not remote_field.multiple:
remote_field.set_cached_value(value, instance)
class ForwardOneToOneDescriptor(ForwardManyToOneDescriptor):
@ -308,8 +309,9 @@ class ReverseOneToOneDescriptor:
"""
def __init__(self, related):
# Following the example above, `related` is an instance of OneToOneRel
# which represents the reverse restaurant field (place.restaurant).
self.related = related
self.cache_name = related.get_cache_name()
@cached_property
def RelatedObjectDoesNotExist(self):
@ -322,7 +324,7 @@ class ReverseOneToOneDescriptor:
)
def is_cached(self, instance):
return hasattr(instance, self.cache_name)
return self.related.is_cached(instance)
def get_queryset(self, **hints):
return self.related.related_model._base_manager.db_manager(hints=hints).all()
@ -343,11 +345,10 @@ class ReverseOneToOneDescriptor:
# Since we're going to assign directly in the cache,
# we must manage the reverse relation cache manually.
rel_obj_cache_name = self.related.field.get_cache_name()
for rel_obj in queryset:
instance = instances_dict[rel_obj_attr(rel_obj)]
setattr(rel_obj, rel_obj_cache_name, instance)
return queryset, rel_obj_attr, instance_attr, True, self.cache_name
self.related.field.set_cached_value(rel_obj, instance)
return queryset, rel_obj_attr, instance_attr, True, self.related.get_cache_name(), False
def __get__(self, instance, cls=None):
"""
@ -364,12 +365,12 @@ class ReverseOneToOneDescriptor:
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
# The related instance is loaded from the database and then cached
# by the field on the model instance state. It can also be pre-cached
# by the forward accessor (ForwardManyToOneDescriptor).
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
rel_obj = self.related.get_cached_value(instance)
except KeyError:
related_pk = instance.pk
if related_pk is None:
rel_obj = None
@ -383,8 +384,8 @@ class ReverseOneToOneDescriptor:
# 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)
self.related.field.set_cached_value(rel_obj, instance)
self.related.set_cached_value(instance, rel_obj)
if rel_obj is None:
raise self.RelatedObjectDoesNotExist(
@ -415,11 +416,17 @@ class ReverseOneToOneDescriptor:
if value is None:
# Update the cached related instance (if any) & clear the cache.
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
# Following the example above, this would be the cached
# ``restaurant`` instance (if any).
rel_obj = self.related.get_cached_value(instance)
except KeyError:
pass
else:
delattr(instance, self.cache_name)
# Remove the ``restaurant`` instance from the ``place``
# instance cache.
self.related.delete_cached_value(instance)
# Set the ``place`` field on the ``restaurant``
# instance to None.
setattr(rel_obj, self.related.field.name, None)
elif not isinstance(value, self.related.related_model):
# An object must be an instance of the related class.
@ -447,11 +454,11 @@ class ReverseOneToOneDescriptor:
# Set the related instance cache used by __get__ to avoid an SQL query
# when accessing the attribute we just set.
setattr(instance, self.cache_name, value)
self.related.set_cached_value(instance, 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)
self.related.field.set_cached_value(value, instance)
class ReverseManyToOneDescriptor:
@ -584,7 +591,7 @@ def create_reverse_many_to_one_manager(superclass, rel):
instance = instances_dict[rel_obj_attr(rel_obj)]
setattr(rel_obj, self.field.name, instance)
cache_name = self.field.related_query_name()
return queryset, rel_obj_attr, instance_attr, False, cache_name
return queryset, rel_obj_attr, instance_attr, False, cache_name, False
def add(self, *objs, bulk=True):
self._remove_prefetched_objects()
@ -882,6 +889,7 @@ def create_forward_many_to_many_manager(superclass, rel, reverse):
),
False,
self.prefetch_cache_name,
False,
)
def add(self, *objs):

13
django/db/models/fields/reverse_related.py
View File

@ -13,9 +13,10 @@ from django.core import exceptions
from django.utils.functional import cached_property
from . import BLANK_CHOICE_DASH
from .mixins import FieldCacheMixin
class ForeignObjectRel:
class ForeignObjectRel(FieldCacheMixin):
"""
Used by ForeignObject to store information about the relation.
@ -162,12 +163,16 @@ class ForeignObjectRel:
return self.related_name
return opts.model_name + ('_set' if self.multiple else '')
def get_cache_name(self):
return "_%s_cache" % self.get_accessor_name()
def get_path_info(self):
return self.field.get_reverse_path_info()
def get_cache_name(self):
"""
Return the name of the cache key to use for storing an instance of the
forward model on the reverse model.
"""
return self.get_accessor_name()
class ManyToOneRel(ForeignObjectRel):
"""

43
django/db/models/query.py
View File

@ -72,7 +72,7 @@ class ModelIterable(BaseIterable):
if queryset._known_related_objects:
for field, rel_objs in queryset._known_related_objects.items():
# Avoid overwriting objects loaded e.g. by select_related
if hasattr(obj, field.get_cache_name()):
if field.is_cached(obj):
continue
pk = getattr(obj, field.get_attname())
try:
@ -1544,12 +1544,13 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
# callable that gets value to be matched for returned instances,
# callable that gets value to be matched for passed in instances,
# boolean that is True for singly related objects,
# cache name to assign to).
# cache or field name to assign to,
# boolean that is True when the previous argument is a cache name vs a field name).
# The 'values to be matched' must be hashable as they will be used
# in a dictionary.
rel_qs, rel_obj_attr, instance_attr, single, cache_name = (
rel_qs, rel_obj_attr, instance_attr, single, cache_name, is_descriptor = (
prefetcher.get_prefetch_queryset(instances, lookup.get_current_queryset(level)))
# We have to handle the possibility that the QuerySet we just got back
# contains some prefetch_related lookups. We don't want to trigger the
@ -1597,8 +1598,18 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
if single:
val = vals[0] if vals else None
to_attr = to_attr if as_attr else cache_name
if as_attr:
# A to_attr has been given for the prefetch.
setattr(obj, to_attr, val)
elif is_descriptor:
# cache_name points to a field name in obj.
# This field is a descriptor for a related object.
setattr(obj, cache_name, val)
else:
# No to_attr has been given for this prefetch operation and the
# cache_name does not point to a descriptor. Store the value of
# the field in the object's field cache.
obj._state.fields_cache[cache_name] = val
else:
if as_attr:
setattr(obj, to_attr, vals)
@ -1653,9 +1664,9 @@ class RelatedPopulator:
# model's fields.
# - related_populators: a list of RelatedPopulator instances if
# select_related() descends to related models from this model.
# - cache_name, reverse_cache_name: the names to use for setattr
# when assigning the fetched object to the from_obj. If the
# reverse_cache_name is set, then we also set the reverse link.
# - field, remote_field: the fields to use for populating the
# internal fields cache. If remote_field is set then we also
# set the reverse link.
select_fields = klass_info['select_fields']
from_parent = klass_info['from_parent']
if not from_parent:
@ -1674,16 +1685,16 @@ class RelatedPopulator:
self.model_cls = klass_info['model']
self.pk_idx = self.init_list.index(self.model_cls._meta.pk.attname)
self.related_populators = get_related_populators(klass_info, select, self.db)
field = klass_info['field']
reverse = klass_info['reverse']
self.reverse_cache_name = None
field = klass_info['field']
self.remote_field = None
if reverse:
self.cache_name = field.remote_field.get_cache_name()
self.reverse_cache_name = field.get_cache_name()
self.field = field.remote_field
self.remote_field = field
else:
self.cache_name = field.get_cache_name()
self.field = field
if field.unique:
self.reverse_cache_name = field.remote_field.get_cache_name()
self.remote_field = field.remote_field
def populate(self, row, from_obj):
if self.reorder_for_init:
@ -1697,9 +1708,9 @@ class RelatedPopulator:
if obj and self.related_populators:
for rel_iter in self.related_populators:
rel_iter.populate(row, obj)
setattr(from_obj, self.cache_name, obj)
if obj and self.reverse_cache_name:
setattr(obj, self.reverse_cache_name, from_obj)
self.field.set_cached_value(from_obj, obj)
if obj and self.remote_field:
self.remote_field.set_cached_value(obj, from_obj)
def get_related_populators(klass_info, select, db):

4
tests/foreign_object/models/article.py
View File

@ -10,9 +10,9 @@ class ArticleTranslationDescriptor(ForwardManyToOneDescriptor):
def __set__(self, instance, value):
if instance is None:
raise AttributeError("%s must be accessed via instance" % self.field.name)
setattr(instance, self.cache_name, value)
self.field.set_cached_value(instance, value)
if value is not None and not self.field.remote_field.multiple:
setattr(value, self.field.related.get_cache_name(), instance)
self.field.remote_field.set_cached_value(value, instance)
class ColConstraint:

2
tests/many_to_one/tests.py
View File

@ -461,7 +461,7 @@ class ManyToOneTests(TestCase):
self.assertIs(c.parent, p)
# But if we kill the cache, we get a new object.
del c._parent_cache
del c._state.fields_cache['parent']
self.assertIsNot(c.parent, p)
# Assigning a new object results in that object getting cached immediately.

2
tests/one_to_one/tests.py
View File

@ -207,7 +207,7 @@ class OneToOneTests(TestCase):
self.assertIs(p.restaurant, r)
# But if we kill the cache, we get a new object
del p._restaurant_cache
del p._state.fields_cache['restaurant']
self.assertIsNot(p.restaurant, r)
# Reassigning the Restaurant object results in an immediate cache update