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# ext/instrumentation.py
# Copyright (C) 2005-2024 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
# mypy: ignore-errors
"""Extensible class instrumentation.
The :mod:`sqlalchemy.ext.instrumentation` package provides for alternate
systems of class instrumentation within the ORM. Class instrumentation
refers to how the ORM places attributes on the class which maintain
data and track changes to that data, as well as event hooks installed
on the class.
.. note::
The extension package is provided for the benefit of integration
with other object management packages, which already perform
their own instrumentation. It is not intended for general use.
For examples of how the instrumentation extension is used,
see the example :ref:`examples_instrumentation`.
"""
import weakref
from .. import util
from ..orm import attributes
from ..orm import base as orm_base
from ..orm import collections
from ..orm import exc as orm_exc
from ..orm import instrumentation as orm_instrumentation
from ..orm import util as orm_util
from ..orm.instrumentation import _default_dict_getter
from ..orm.instrumentation import _default_manager_getter
from ..orm.instrumentation import _default_opt_manager_getter
from ..orm.instrumentation import _default_state_getter
from ..orm.instrumentation import ClassManager
from ..orm.instrumentation import InstrumentationFactory
INSTRUMENTATION_MANAGER = "__sa_instrumentation_manager__"
"""Attribute, elects custom instrumentation when present on a mapped class.
Allows a class to specify a slightly or wildly different technique for
tracking changes made to mapped attributes and collections.
Only one instrumentation implementation is allowed in a given object
inheritance hierarchy.
The value of this attribute must be a callable and will be passed a class
object. The callable must return one of:
- An instance of an :class:`.InstrumentationManager` or subclass
- An object implementing all or some of InstrumentationManager (TODO)
- A dictionary of callables, implementing all or some of the above (TODO)
- An instance of a :class:`.ClassManager` or subclass
This attribute is consulted by SQLAlchemy instrumentation
resolution, once the :mod:`sqlalchemy.ext.instrumentation` module
has been imported. If custom finders are installed in the global
instrumentation_finders list, they may or may not choose to honor this
attribute.
"""
def find_native_user_instrumentation_hook(cls):
"""Find user-specified instrumentation management for a class."""
return getattr(cls, INSTRUMENTATION_MANAGER, None)
instrumentation_finders = [find_native_user_instrumentation_hook]
"""An extensible sequence of callables which return instrumentation
implementations
When a class is registered, each callable will be passed a class object.
If None is returned, the
next finder in the sequence is consulted. Otherwise the return must be an
instrumentation factory that follows the same guidelines as
sqlalchemy.ext.instrumentation.INSTRUMENTATION_MANAGER.
By default, the only finder is find_native_user_instrumentation_hook, which
searches for INSTRUMENTATION_MANAGER. If all finders return None, standard
ClassManager instrumentation is used.
"""
class ExtendedInstrumentationRegistry(InstrumentationFactory):
"""Extends :class:`.InstrumentationFactory` with additional
bookkeeping, to accommodate multiple types of
class managers.
"""
_manager_finders = weakref.WeakKeyDictionary()
_state_finders = weakref.WeakKeyDictionary()
_dict_finders = weakref.WeakKeyDictionary()
_extended = False
def _locate_extended_factory(self, class_):
for finder in instrumentation_finders:
factory = finder(class_)
if factory is not None:
manager = self._extended_class_manager(class_, factory)
return manager, factory
else:
return None, None
def _check_conflicts(self, class_, factory):
existing_factories = self._collect_management_factories_for(
class_
).difference([factory])
if existing_factories:
raise TypeError(
"multiple instrumentation implementations specified "
"in %s inheritance hierarchy: %r"
% (class_.__name__, list(existing_factories))
)
def _extended_class_manager(self, class_, factory):
manager = factory(class_)
if not isinstance(manager, ClassManager):
manager = _ClassInstrumentationAdapter(class_, manager)
if factory != ClassManager and not self._extended:
# somebody invoked a custom ClassManager.
# reinstall global "getter" functions with the more
# expensive ones.
self._extended = True
_install_instrumented_lookups()
self._manager_finders[class_] = manager.manager_getter()
self._state_finders[class_] = manager.state_getter()
self._dict_finders[class_] = manager.dict_getter()
return manager
def _collect_management_factories_for(self, cls):
"""Return a collection of factories in play or specified for a
hierarchy.
Traverses the entire inheritance graph of a cls and returns a
collection of instrumentation factories for those classes. Factories
are extracted from active ClassManagers, if available, otherwise
instrumentation_finders is consulted.
"""
hierarchy = util.class_hierarchy(cls)
factories = set()
for member in hierarchy:
manager = self.opt_manager_of_class(member)
if manager is not None:
factories.add(manager.factory)
else:
for finder in instrumentation_finders:
factory = finder(member)
if factory is not None:
break
else:
factory = None
factories.add(factory)
factories.discard(None)
return factories
def unregister(self, class_):
super().unregister(class_)
if class_ in self._manager_finders:
del self._manager_finders[class_]
del self._state_finders[class_]
del self._dict_finders[class_]
def opt_manager_of_class(self, cls):
try:
finder = self._manager_finders.get(
cls, _default_opt_manager_getter
)
except TypeError:
# due to weakref lookup on invalid object
return None
else:
return finder(cls)
def manager_of_class(self, cls):
try:
finder = self._manager_finders.get(cls, _default_manager_getter)
except TypeError:
# due to weakref lookup on invalid object
raise orm_exc.UnmappedClassError(
cls, f"Can't locate an instrumentation manager for class {cls}"
)
else:
manager = finder(cls)
if manager is None:
raise orm_exc.UnmappedClassError(
cls,
f"Can't locate an instrumentation manager for class {cls}",
)
return manager
def state_of(self, instance):
if instance is None:
raise AttributeError("None has no persistent state.")
return self._state_finders.get(
instance.__class__, _default_state_getter
)(instance)
def dict_of(self, instance):
if instance is None:
raise AttributeError("None has no persistent state.")
return self._dict_finders.get(
instance.__class__, _default_dict_getter
)(instance)
orm_instrumentation._instrumentation_factory = _instrumentation_factory = (
ExtendedInstrumentationRegistry()
)
orm_instrumentation.instrumentation_finders = instrumentation_finders
class InstrumentationManager:
"""User-defined class instrumentation extension.
:class:`.InstrumentationManager` can be subclassed in order
to change
how class instrumentation proceeds. This class exists for
the purposes of integration with other object management
frameworks which would like to entirely modify the
instrumentation methodology of the ORM, and is not intended
for regular usage. For interception of class instrumentation
events, see :class:`.InstrumentationEvents`.
The API for this class should be considered as semi-stable,
and may change slightly with new releases.
"""
# r4361 added a mandatory (cls) constructor to this interface.
# given that, perhaps class_ should be dropped from all of these
# signatures.
def __init__(self, class_):
pass
def manage(self, class_, manager):
setattr(class_, "_default_class_manager", manager)
def unregister(self, class_, manager):
delattr(class_, "_default_class_manager")
def manager_getter(self, class_):
def get(cls):
return cls._default_class_manager
return get
def instrument_attribute(self, class_, key, inst):
pass
def post_configure_attribute(self, class_, key, inst):
pass
def install_descriptor(self, class_, key, inst):
setattr(class_, key, inst)
def uninstall_descriptor(self, class_, key):
delattr(class_, key)
def install_member(self, class_, key, implementation):
setattr(class_, key, implementation)
def uninstall_member(self, class_, key):
delattr(class_, key)
def instrument_collection_class(self, class_, key, collection_class):
return collections.prepare_instrumentation(collection_class)
def get_instance_dict(self, class_, instance):
return instance.__dict__
def initialize_instance_dict(self, class_, instance):
pass
def install_state(self, class_, instance, state):
setattr(instance, "_default_state", state)
def remove_state(self, class_, instance):
delattr(instance, "_default_state")
def state_getter(self, class_):
return lambda instance: getattr(instance, "_default_state")
def dict_getter(self, class_):
return lambda inst: self.get_instance_dict(class_, inst)
class _ClassInstrumentationAdapter(ClassManager):
"""Adapts a user-defined InstrumentationManager to a ClassManager."""
def __init__(self, class_, override):
self._adapted = override
self._get_state = self._adapted.state_getter(class_)
self._get_dict = self._adapted.dict_getter(class_)
ClassManager.__init__(self, class_)
def manage(self):
self._adapted.manage(self.class_, self)
def unregister(self):
self._adapted.unregister(self.class_, self)
def manager_getter(self):
return self._adapted.manager_getter(self.class_)
def instrument_attribute(self, key, inst, propagated=False):
ClassManager.instrument_attribute(self, key, inst, propagated)
if not propagated:
self._adapted.instrument_attribute(self.class_, key, inst)
def post_configure_attribute(self, key):
super().post_configure_attribute(key)
self._adapted.post_configure_attribute(self.class_, key, self[key])
def install_descriptor(self, key, inst):
self._adapted.install_descriptor(self.class_, key, inst)
def uninstall_descriptor(self, key):
self._adapted.uninstall_descriptor(self.class_, key)
def install_member(self, key, implementation):
self._adapted.install_member(self.class_, key, implementation)
def uninstall_member(self, key):
self._adapted.uninstall_member(self.class_, key)
def instrument_collection_class(self, key, collection_class):
return self._adapted.instrument_collection_class(
self.class_, key, collection_class
)
def initialize_collection(self, key, state, factory):
delegate = getattr(self._adapted, "initialize_collection", None)
if delegate:
return delegate(key, state, factory)
else:
return ClassManager.initialize_collection(
self, key, state, factory
)
def new_instance(self, state=None):
instance = self.class_.__new__(self.class_)
self.setup_instance(instance, state)
return instance
def _new_state_if_none(self, instance):
"""Install a default InstanceState if none is present.
A private convenience method used by the __init__ decorator.
"""
if self.has_state(instance):
return False
else:
return self.setup_instance(instance)
def setup_instance(self, instance, state=None):
self._adapted.initialize_instance_dict(self.class_, instance)
if state is None:
state = self._state_constructor(instance, self)
# the given instance is assumed to have no state
self._adapted.install_state(self.class_, instance, state)
return state
def teardown_instance(self, instance):
self._adapted.remove_state(self.class_, instance)
def has_state(self, instance):
try:
self._get_state(instance)
except orm_exc.NO_STATE:
return False
else:
return True
def state_getter(self):
return self._get_state
def dict_getter(self):
return self._get_dict
def _install_instrumented_lookups():
"""Replace global class/object management functions
with ExtendedInstrumentationRegistry implementations, which
allow multiple types of class managers to be present,
at the cost of performance.
This function is called only by ExtendedInstrumentationRegistry
and unit tests specific to this behavior.
The _reinstall_default_lookups() function can be called
after this one to re-establish the default functions.
"""
_install_lookups(
dict(
instance_state=_instrumentation_factory.state_of,
instance_dict=_instrumentation_factory.dict_of,
manager_of_class=_instrumentation_factory.manager_of_class,
opt_manager_of_class=_instrumentation_factory.opt_manager_of_class,
)
)
def _reinstall_default_lookups():
"""Restore simplified lookups."""
_install_lookups(
dict(
instance_state=_default_state_getter,
instance_dict=_default_dict_getter,
manager_of_class=_default_manager_getter,
opt_manager_of_class=_default_opt_manager_getter,
)
)
_instrumentation_factory._extended = False
def _install_lookups(lookups):
global instance_state, instance_dict
global manager_of_class, opt_manager_of_class
instance_state = lookups["instance_state"]
instance_dict = lookups["instance_dict"]
manager_of_class = lookups["manager_of_class"]
opt_manager_of_class = lookups["opt_manager_of_class"]
orm_base.instance_state = attributes.instance_state = (
orm_instrumentation.instance_state
) = instance_state
orm_base.instance_dict = attributes.instance_dict = (
orm_instrumentation.instance_dict
) = instance_dict
orm_base.manager_of_class = attributes.manager_of_class = (
orm_instrumentation.manager_of_class
) = manager_of_class
orm_base.opt_manager_of_class = orm_util.opt_manager_of_class = (
attributes.opt_manager_of_class
) = orm_instrumentation.opt_manager_of_class = opt_manager_of_class