name : instrumentation.py """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.instrumentation import _default_dict_getter from ..orm.instrumentation import _default_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.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_): if class_ in self._manager_finders: del self._manager_finders[class_] del self._state_finders[class_] del self._dict_finders[class_] super(ExtendedInstrumentationRegistry, self).unregister(class_) def manager_of_class(self, cls): if cls is None: return None try: finder = self._manager_finders.get(cls, _default_manager_getter) except TypeError: # due to weakref lookup on invalid object return None else: return finder(cls) 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(object): """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 dispose(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 dispose(self): self._adapted.dispose(self.class_) 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(_ClassInstrumentationAdapter, self).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, ) ) 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, ) ) _instrumentation_factory._extended = False def _install_lookups(lookups): global instance_state, instance_dict, manager_of_class instance_state = lookups["instance_state"] instance_dict = lookups["instance_dict"] manager_of_class = lookups["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