# attributes.py - manages object attributes # Copyright (C) 2005, 2006, 2007 Michael Bayer mike_mp@zzzcomputing.com # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php import weakref from sqlalchemy import util from sqlalchemy.orm import util as orm_util, interfaces, collections from sqlalchemy.orm.mapper import class_mapper from sqlalchemy import logging, exceptions PASSIVE_NORESULT = object() ATTR_WAS_SET = object() class InstrumentedAttribute(interfaces.PropComparator): """attribute access for instrumented classes.""" def __init__(self, class_, manager, key, callable_, trackparent=False, extension=None, compare_function=None, mutable_scalars=False, comparator=None, **kwargs): """Construct an InstrumentedAttribute. class_ the class to be instrumented. manager AttributeManager managing this class key string name of the attribute callable_ optional function which generates a callable based on a parent instance, which produces the "default" values for a scalar or collection attribute when it's first accessed, if not present already. trackparent if True, attempt to track if an instance has a parent attached to it via this attribute extension an AttributeExtension object which will receive set/delete/append/remove/etc. events compare_function a function that compares two values which are normally assignable to this attribute mutable_scalars if True, the values which are normally assignable to this attribute can mutate, and need to be compared against a copy of their original contents in order to detect changes on the parent instance comparator a sql.Comparator to which class-level compare/math events will be sent """ self.class_ = class_ self.manager = manager self.key = key self.callable_ = callable_ self.trackparent = trackparent self.mutable_scalars = mutable_scalars self.comparator = comparator self.copy = None if compare_function is None: self.is_equal = lambda x,y: x == y else: self.is_equal = compare_function self.extensions = util.to_list(extension or []) def __set__(self, obj, value): self.set(obj, value, None) def __delete__(self, obj): self.delete(None, obj) def __get__(self, obj, owner): if obj is None: return self return self.get(obj) def clause_element(self): return self.comparator.clause_element() def operate(self, op, other): return op(self.comparator, other) def reverse_operate(self, op, other): return op(other, self.comparator) def hasparent(self, item, optimistic=False): """Return the boolean value of a `hasparent` flag attached to the given item. The `optimistic` flag determines what the default return value should be if no `hasparent` flag can be located. As this function is used to determine if an instance is an *orphan*, instances that were loaded from storage should be assumed to not be orphans, until a True/False value for this flag is set. An instance attribute that is loaded by a callable function will also not have a `hasparent` flag. """ return item._state.get(('hasparent', id(self)), optimistic) def sethasparent(self, item, value): """Set a boolean flag on the given item corresponding to whether or not it is attached to a parent object via the attribute represented by this ``InstrumentedAttribute``. """ item._state[('hasparent', id(self))] = value def get_history(self, obj, passive=False): """Return a new ``AttributeHistory`` object for the given object/this attribute's key. If `passive` is True, then don't execute any callables; if the attribute's value can only be achieved via executing a callable, then return None. """ # get the current state. this may trigger a lazy load if # passive is False. current = self.get(obj, passive=passive) if current is PASSIVE_NORESULT: return None return AttributeHistory(self, obj, current, passive=passive) def set_callable(self, obj, callable_): """Set a callable function for this attribute on the given object. This callable will be executed when the attribute is next accessed, and is assumed to construct part of the instances previously stored state. When its value or values are loaded, they will be established as part of the instance's *committed state*. While *trackparent* information will be assembled for these instances, attribute-level event handlers will not be fired. The callable overrides the class level callable set in the ``InstrumentedAttribute` constructor. """ if callable_ is None: self.initialize(obj) else: obj._state[('callable', self)] = callable_ def _get_callable(self, obj): if ('callable', self) in obj._state: return obj._state[('callable', self)] elif self.callable_ is not None: return self.callable_(obj) else: return None def reset(self, obj): """Remove any per-instance callable functions corresponding to this ``InstrumentedAttribute``'s attribute from the given object, and remove this ``InstrumentedAttribute``'s attribute from the given object's dictionary. """ try: del obj._state[('callable', self)] except KeyError: pass self.clear(obj) def clear(self, obj): """Remove this ``InstrumentedAttribute``'s attribute from the given object's dictionary. Subsequent calls to ``getattr(obj, key)`` will raise an ``AttributeError`` by default. """ try: del obj.__dict__[self.key] except KeyError: pass def check_mutable_modified(self, obj): return False def initialize(self, obj): """Initialize this attribute on the given object instance with an empty value.""" obj.__dict__[self.key] = None return None def get(self, obj, passive=False): """Retrieve a value from the given object. If a callable is assembled on this object's attribute, and passive is False, the callable will be executed and the resulting value will be set as the new value for this attribute. """ try: return obj.__dict__[self.key] except KeyError: state = obj._state # if an instance-wide "trigger" was set, call that # and start again if 'trigger' in state: trig = state['trigger'] del state['trigger'] trig() return self.get(obj, passive=passive) callable_ = self._get_callable(obj) if callable_ is not None: if passive: return PASSIVE_NORESULT self.logger.debug("Executing lazy callable on %s.%s" % (orm_util.instance_str(obj), self.key)) value = callable_() if value is not ATTR_WAS_SET: return self.set_committed_value(obj, value) else: return obj.__dict__[self.key] else: # Return a new, empty value return self.initialize(obj) def append(self, obj, value, initiator): self.set(obj, value, initiator) def remove(self, obj, value, initiator): self.set(obj, None, initiator) def set(self, obj, value, initiator): raise NotImplementedError() def set_committed_value(self, obj, value): """set an attribute value on the given instance and 'commit' it. this indicates that the given value is the "persisted" value, and history will be logged only if a newly set value is not equal to this value. this is typically used by deferred/lazy attribute loaders to set object attributes after the initial load. """ state = obj._state orig = state.get('original', None) if orig is not None: orig.commit_attribute(self, obj, value) # remove per-instance callable, if any state.pop(('callable', self), None) obj.__dict__[self.key] = value return value def set_raw_value(self, obj, value): obj.__dict__[self.key] = value return value def fire_append_event(self, obj, value, initiator): obj._state['modified'] = True if self.trackparent and value is not None: self.sethasparent(value, True) for ext in self.extensions: ext.append(obj, value, initiator or self) def fire_remove_event(self, obj, value, initiator): obj._state['modified'] = True if self.trackparent and value is not None: self.sethasparent(value, False) for ext in self.extensions: ext.remove(obj, value, initiator or self) def fire_replace_event(self, obj, value, previous, initiator): obj._state['modified'] = True if self.trackparent: if value is not None: self.sethasparent(value, True) if previous is not None: self.sethasparent(previous, False) for ext in self.extensions: ext.set(obj, value, previous, initiator or self) property = property(lambda s: class_mapper(s.class_).get_property(s.key), doc="the MapperProperty object associated with this attribute") InstrumentedAttribute.logger = logging.class_logger(InstrumentedAttribute) class InstrumentedScalarAttribute(InstrumentedAttribute): """represents a scalar-holding InstrumentedAttribute.""" def __init__(self, class_, manager, key, callable_, trackparent=False, extension=None, copy_function=None, compare_function=None, mutable_scalars=False, **kwargs): super(InstrumentedScalarAttribute, self).__init__(class_, manager, key, callable_, trackparent=trackparent, extension=extension, compare_function=compare_function, **kwargs) self.mutable_scalars = mutable_scalars if copy_function is None: copy_function = self.__copy self.copy = copy_function def __copy(self, item): # scalar values are assumed to be immutable unless a copy function # is passed return item def __delete__(self, obj): old = self.get(obj) del obj.__dict__[self.key] self.fire_remove_event(obj, old, self) def check_mutable_modified(self, obj): if self.mutable_scalars: h = self.get_history(obj, passive=True) if h is not None and h.is_modified(): obj._state['modified'] = True return True else: return False else: return False def set(self, obj, value, initiator): """Set a value on the given object. `initiator` is the ``InstrumentedAttribute`` that initiated the ``set()` operation and is used to control the depth of a circular setter operation. """ if initiator is self: return state = obj._state # if an instance-wide "trigger" was set, call that if 'trigger' in state: trig = state['trigger'] del state['trigger'] trig() old = self.get(obj) obj.__dict__[self.key] = value self.fire_replace_event(obj, value, old, initiator) type = property(lambda self: self.property.columns[0].type) class InstrumentedCollectionAttribute(InstrumentedAttribute): """A collection-holding attribute that instruments changes in membership. InstrumentedCollectionAttribute holds an arbitrary, user-specified container object (defaulting to a list) and brokers access to the CollectionAdapter, a "view" onto that object that presents consistent bag semantics to the orm layer independent of the user data implementation. """ def __init__(self, class_, manager, key, callable_, typecallable=None, trackparent=False, extension=None, copy_function=None, compare_function=None, **kwargs): super(InstrumentedCollectionAttribute, self).__init__(class_, manager, key, callable_, trackparent=trackparent, extension=extension, compare_function=compare_function, **kwargs) if copy_function is None: copy_function = self.__copy self.copy = copy_function if typecallable is None: typecallable = list self.collection_factory = \ collections._prepare_instrumentation(typecallable) self.collection_interface = \ util.duck_type_collection(self.collection_factory()) def __copy(self, item): return [y for y in list(collections.collection_adapter(item))] def __set__(self, obj, value): """Replace the current collection with a new one.""" setting_type = util.duck_type_collection(value) if value is None or setting_type != self.collection_interface: raise exceptions.ArgumentError( "Incompatible collection type on assignment: %s is not %s-like" % (type(value).__name__, self.collection_interface.__name__)) if hasattr(value, '_sa_adapter'): self.set(obj, list(getattr(value, '_sa_adapter')), None) elif setting_type == dict: self.set(obj, value.values(), None) else: self.set(obj, value, None) def __delete__(self, obj): if self.key not in obj.__dict__: return obj._state['modified'] = True collection = self._get_collection(obj) collection.clear_with_event() del obj.__dict__[self.key] def initialize(self, obj): """Initialize this attribute on the given object instance with an empty collection.""" _, user_data = self._build_collection(obj) obj.__dict__[self.key] = user_data return user_data def append(self, obj, value, initiator): if initiator is self: return collection = self._get_collection(obj) collection.append_with_event(value, initiator) def remove(self, obj, value, initiator): if initiator is self: return collection = self._get_collection(obj) collection.remove_with_event(value, initiator) def set(self, obj, value, initiator): """Set a value on the given object. `initiator` is the ``InstrumentedAttribute`` that initiated the ``set()` operation and is used to control the depth of a circular setter operation. """ if initiator is self: return state = obj._state # if an instance-wide "trigger" was set, call that if 'trigger' in state: trig = state['trigger'] del state['trigger'] trig() old = self.get(obj) old_collection = self._get_collection(obj, old) new_collection, user_data = self._build_collection(obj) self._load_collection(obj, value or [], emit_events=True, collection=new_collection) obj.__dict__[self.key] = user_data state['modified'] = True # mark all the old elements as detached from the parent if old_collection: old_collection.clear_with_event() old_collection.unlink(old) def set_committed_value(self, obj, value): """Set an attribute value on the given instance and 'commit' it.""" state = obj._state orig = state.get('original', None) collection, user_data = self._build_collection(obj) self._load_collection(obj, value or [], emit_events=False, collection=collection) value = user_data if orig is not None: orig.commit_attribute(self, obj, value) # remove per-instance callable, if any state.pop(('callable', self), None) obj.__dict__[self.key] = value return value def _build_collection(self, obj): user_data = self.collection_factory() collection = collections.CollectionAdapter(self, obj, user_data) return collection, user_data def _load_collection(self, obj, values, emit_events=True, collection=None): collection = collection or self._get_collection(obj) if values is None: return elif emit_events: for item in values: collection.append_with_event(item) else: for item in values: collection.append_without_event(item) def _get_collection(self, obj, user_data=None): if user_data is None: user_data = self.get(obj) try: return getattr(user_data, '_sa_adapter') except AttributeError: collections.CollectionAdapter(self, obj, user_data) return getattr(user_data, '_sa_adapter') class GenericBackrefExtension(interfaces.AttributeExtension): """An extension which synchronizes a two-way relationship. A typical two-way relationship is a parent object containing a list of child objects, where each child object references the parent. The other are two objects which contain scalar references to each other. """ def __init__(self, key): self.key = key def set(self, obj, child, oldchild, initiator): if oldchild is child: return if oldchild is not None: getattr(oldchild.__class__, self.key).remove(oldchild, obj, initiator) if child is not None: getattr(child.__class__, self.key).append(child, obj, initiator) def append(self, obj, child, initiator): getattr(child.__class__, self.key).append(child, obj, initiator) def remove(self, obj, child, initiator): getattr(child.__class__, self.key).remove(child, obj, initiator) class CommittedState(object): """Store the original state of an object when the ``commit()` method on the attribute manager is called. """ NO_VALUE = object() def __init__(self, manager, obj): self.data = {} for attr in manager.managed_attributes(obj.__class__): self.commit_attribute(attr, obj) def commit_attribute(self, attr, obj, value=NO_VALUE): """Establish the value of attribute `attr` on instance `obj` as *committed*. This corresponds to a previously saved state being restored. """ if value is CommittedState.NO_VALUE: if attr.key in obj.__dict__: value = obj.__dict__[attr.key] if value is not CommittedState.NO_VALUE: self.data[attr.key] = attr.copy(value) # not tracking parent on lazy-loaded instances at the moment. # its not needed since they will be "optimistically" tested #if attr.uselist: #if attr.trackparent: # [attr.sethasparent(x, True) for x in self.data[attr.key] if x is not None] #else: #if attr.trackparent and value is not None: # attr.sethasparent(value, True) def rollback(self, manager, obj): for attr in manager.managed_attributes(obj.__class__): if self.data.has_key(attr.key): if not isinstance(attr, InstrumentedCollectionAttribute): obj.__dict__[attr.key] = self.data[attr.key] else: collection = attr._get_collection(obj) collection.clear_without_event() for item in self.data[attr.key]: collection.append_without_event(item) else: del obj.__dict__[attr.key] def __repr__(self): return "CommittedState: %s" % repr(self.data) class AttributeHistory(object): """Calculate the *history* of a particular attribute on a particular instance, based on the ``CommittedState`` associated with the instance, if any. """ def __init__(self, attr, obj, current, passive=False): self.attr = attr # get the "original" value. if a lazy load was fired when we got # the 'current' value, this "original" was also populated just # now as well (therefore we have to get it second) orig = obj._state.get('original', None) if orig is not None: original = orig.data.get(attr.key) else: original = None if isinstance(attr, InstrumentedCollectionAttribute): self._current = current s = util.Set(original or []) self._added_items = [] self._unchanged_items = [] self._deleted_items = [] if current: collection = attr._get_collection(obj, current) for a in collection: if a in s: self._unchanged_items.append(a) else: self._added_items.append(a) for a in s: if a not in self._unchanged_items: self._deleted_items.append(a) else: self._current = [current] if attr.is_equal(current, original): self._unchanged_items = [current] self._added_items = [] self._deleted_items = [] else: self._added_items = [current] if original is not None: self._deleted_items = [original] else: self._deleted_items = [] self._unchanged_items = [] def __iter__(self): return iter(self._current) def is_modified(self): return len(self._deleted_items) > 0 or len(self._added_items) > 0 def added_items(self): return self._added_items def unchanged_items(self): return self._unchanged_items def deleted_items(self): return self._deleted_items def hasparent(self, obj): """Deprecated. This should be called directly from the appropriate ``InstrumentedAttribute`` object. """ return self.attr.hasparent(obj) class AttributeManager(object): """Allow the instrumentation of object attributes.""" def __init__(self): # will cache attributes, indexed by class objects self._inherited_attribute_cache = weakref.WeakKeyDictionary() self._noninherited_attribute_cache = weakref.WeakKeyDictionary() def clear_attribute_cache(self): self._attribute_cache.clear() def rollback(self, *obj): """Retrieve the committed history for each object in the given list, and rolls back the attributes each instance to their original value. """ for o in obj: orig = o._state.get('original') if orig is not None: orig.rollback(self, o) else: self._clear(o) def _clear(self, obj): for attr in self.managed_attributes(obj.__class__): try: del obj.__dict__[attr.key] except KeyError: pass def commit(self, *obj): """Create a ``CommittedState`` instance for each object in the given list, representing its *unchanged* state, and associates it with the instance. ``AttributeHistory`` objects will indicate the modified state of instance attributes as compared to its value in this ``CommittedState`` object. """ for o in obj: o._state['original'] = CommittedState(self, o) o._state['modified'] = False def managed_attributes(self, class_): """Return a list of all ``InstrumentedAttribute`` objects associated with the given class. """ try: return self._inherited_attribute_cache[class_] except KeyError: if not isinstance(class_, type): raise TypeError(repr(class_) + " is not a type") inherited = [v for v in [getattr(class_, key, None) for key in dir(class_)] if isinstance(v, InstrumentedAttribute)] self._inherited_attribute_cache[class_] = inherited return inherited def noninherited_managed_attributes(self, class_): try: return self._noninherited_attribute_cache[class_] except KeyError: if not isinstance(class_, type): raise TypeError(repr(class_) + " is not a type") noninherited = [v for v in [getattr(class_, key, None) for key in list(class_.__dict__)] if isinstance(v, InstrumentedAttribute)] self._noninherited_attribute_cache[class_] = noninherited return noninherited def is_modified(self, object): for attr in self.managed_attributes(object.__class__): if attr.check_mutable_modified(object): return True return object._state.get('modified', False) def init_attr(self, obj): """Sets up the __sa_attr_state dictionary on the given instance. This dictionary is automatically created when the `_state` attribute of the class is first accessed, but calling it here will save a single throw of an ``AttributeError`` that occurs in that creation step. """ setattr(obj, '_%s__sa_attr_state' % obj.__class__.__name__, {}) def get_history(self, obj, key, **kwargs): """Return a new ``AttributeHistory`` object for the given attribute on the given object. """ return getattr(obj.__class__, key).get_history(obj, **kwargs) def get_as_list(self, obj, key, passive=False): """Return an attribute of the given name from the given object. If the attribute is a scalar, return it as a single-item list, otherwise return a collection based attribute. If the attribute's value is to be produced by an unexecuted callable, the callable will only be executed if the given `passive` flag is False. """ attr = getattr(obj.__class__, key) x = attr.get(obj, passive=passive) if x is PASSIVE_NORESULT: return [] elif isinstance(attr, InstrumentedCollectionAttribute): return list(attr._get_collection(obj, x)) else: return [x] def trigger_history(self, obj, callable): """Clear all managed object attributes and places the given `callable` as an attribute-wide *trigger*, which will execute upon the next attribute access, after which the trigger is removed. """ self._clear(obj) try: del obj._state['original'] except KeyError: pass obj._state['trigger'] = callable def untrigger_history(self, obj): """Remove a trigger function set by trigger_history. Does not restore the previous state of the object. """ del obj._state['trigger'] def has_trigger(self, obj): """Return True if the given object has a trigger function set by ``trigger_history()``. """ return 'trigger' in obj._state def reset_instance_attribute(self, obj, key): """Remove any per-instance callable functions corresponding to given attribute `key` from the given object, and remove this attribute from the given object's dictionary. """ attr = getattr(obj.__class__, key) attr.reset(obj) def reset_class_managed(self, class_): """Remove all ``InstrumentedAttribute`` property objects from the given class. """ for attr in self.noninherited_managed_attributes(class_): delattr(class_, attr.key) self._inherited_attribute_cache.pop(class_,None) self._noninherited_attribute_cache.pop(class_,None) def is_class_managed(self, class_, key): """Return True if the given `key` correponds to an instrumented property on the given class. """ return hasattr(class_, key) and isinstance(getattr(class_, key), InstrumentedAttribute) def init_instance_attribute(self, obj, key, callable_=None): """Initialize an attribute on an instance to either a blank value, cancelling out any class- or instance-level callables that were present, or if a `callable` is supplied set the callable to be invoked when the attribute is next accessed. """ getattr(obj.__class__, key).set_callable(obj, callable_) def create_prop(self, class_, key, uselist, callable_, typecallable, **kwargs): """Create a scalar property object, defaulting to ``InstrumentedAttribute``, which will communicate change events back to this ``AttributeManager``. """ if uselist: return InstrumentedCollectionAttribute(class_, self, key, callable_, typecallable, **kwargs) else: return InstrumentedScalarAttribute(class_, self, key, callable_, **kwargs) def get_attribute(self, obj_or_cls, key): """Register an attribute at the class level to be instrumented for all instances of the class. """ if isinstance(obj_or_cls, type): return getattr(obj_or_cls, key) else: return getattr(obj_or_cls.__class__, key) def register_attribute(self, class_, key, uselist, callable_=None, **kwargs): """Register an attribute at the class level to be instrumented for all instances of the class. """ # firt invalidate the cache for the given class # (will be reconstituted as needed, while getting managed attributes) self._inherited_attribute_cache.pop(class_, None) self._noninherited_attribute_cache.pop(class_, None) if not hasattr(class_, '_state'): def _get_state(self): if not hasattr(self, '_sa_attr_state'): self._sa_attr_state = {} return self._sa_attr_state class_._state = property(_get_state) typecallable = kwargs.pop('typecallable', None) if isinstance(typecallable, InstrumentedAttribute): typecallable = None setattr(class_, key, self.create_prop(class_, key, uselist, callable_, typecallable=typecallable, **kwargs)) def init_collection(self, instance, key): """Initialize a collection attribute and return the collection adapter.""" attr = self.get_attribute(instance, key) user_data = attr.initialize(instance) return attr._get_collection(instance, user_data)