1572 lines
62 KiB
Python
1572 lines
62 KiB
Python
# orm/events.py
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# Copyright (C) 2005-2013 the SQLAlchemy authors and contributors <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: http://www.opensource.org/licenses/mit-license.php
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"""ORM event interfaces.
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"""
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from .. import event, exc, util
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orm = util.importlater("sqlalchemy", "orm")
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import inspect
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import weakref
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class InstrumentationEvents(event.Events):
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"""Events related to class instrumentation events.
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The listeners here support being established against
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any new style class, that is any object that is a subclass
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of 'type'. Events will then be fired off for events
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against that class. If the "propagate=True" flag is passed
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to event.listen(), the event will fire off for subclasses
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of that class as well.
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The Python ``type`` builtin is also accepted as a target,
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which when used has the effect of events being emitted
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for all classes.
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Note the "propagate" flag here is defaulted to ``True``,
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unlike the other class level events where it defaults
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to ``False``. This means that new subclasses will also
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be the subject of these events, when a listener
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is established on a superclass.
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.. versionchanged:: 0.8 - events here will emit based
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on comparing the incoming class to the type of class
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passed to :func:`.event.listen`. Previously, the
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event would fire for any class unconditionally regardless
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of what class was sent for listening, despite
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documentation which stated the contrary.
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"""
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@classmethod
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def _accept_with(cls, target):
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# TODO: there's no coverage for this
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if isinstance(target, type):
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return _InstrumentationEventsHold(target)
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else:
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return None
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@classmethod
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def _listen(cls, target, identifier, fn, propagate=True):
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def listen(target_cls, *arg):
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listen_cls = target()
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if propagate and issubclass(target_cls, listen_cls):
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return fn(target_cls, *arg)
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elif not propagate and target_cls is listen_cls:
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return fn(target_cls, *arg)
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def remove(ref):
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event.Events._remove(orm.instrumentation._instrumentation_factory,
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identifier, listen)
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target = weakref.ref(target.class_, remove)
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event.Events._listen(orm.instrumentation._instrumentation_factory,
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identifier, listen)
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@classmethod
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def _remove(cls, identifier, target, fn):
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raise NotImplementedError("Removal of instrumentation events "
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"not yet implemented")
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@classmethod
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def _clear(cls):
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super(InstrumentationEvents, cls)._clear()
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orm.instrumentation._instrumentation_factory.dispatch._clear()
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def class_instrument(self, cls):
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"""Called after the given class is instrumented.
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To get at the :class:`.ClassManager`, use
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:func:`.manager_of_class`.
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"""
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def class_uninstrument(self, cls):
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"""Called before the given class is uninstrumented.
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To get at the :class:`.ClassManager`, use
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:func:`.manager_of_class`.
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"""
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def attribute_instrument(self, cls, key, inst):
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"""Called when an attribute is instrumented."""
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class _InstrumentationEventsHold(object):
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"""temporary marker object used to transfer from _accept_with() to
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_listen() on the InstrumentationEvents class.
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"""
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def __init__(self, class_):
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self.class_ = class_
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dispatch = event.dispatcher(InstrumentationEvents)
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class InstanceEvents(event.Events):
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"""Define events specific to object lifecycle.
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e.g.::
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from sqlalchemy import event
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def my_load_listener(target, context):
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print "on load!"
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event.listen(SomeClass, 'load', my_load_listener)
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Available targets include:
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* mapped classes
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* unmapped superclasses of mapped or to-be-mapped classes
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(using the ``propagate=True`` flag)
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* :class:`.Mapper` objects
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* the :class:`.Mapper` class itself and the :func:`.mapper`
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function indicate listening for all mappers.
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.. versionchanged:: 0.8.0 instance events can be associated with
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unmapped superclasses of mapped classes.
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Instance events are closely related to mapper events, but
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are more specific to the instance and its instrumentation,
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rather than its system of persistence.
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When using :class:`.InstanceEvents`, several modifiers are
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available to the :func:`.event.listen` function.
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:param propagate=False: When True, the event listener should
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be applied to all inheriting classes as well as the
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class which is the target of this listener.
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:param raw=False: When True, the "target" argument passed
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to applicable event listener functions will be the
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instance's :class:`.InstanceState` management
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object, rather than the mapped instance itself.
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"""
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@classmethod
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def _accept_with(cls, target):
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if isinstance(target, orm.instrumentation.ClassManager):
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return target
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elif isinstance(target, orm.Mapper):
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return target.class_manager
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elif target is orm.mapper:
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return orm.instrumentation.ClassManager
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elif isinstance(target, type):
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if issubclass(target, orm.Mapper):
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return orm.instrumentation.ClassManager
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else:
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manager = orm.instrumentation.manager_of_class(target)
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if manager:
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return manager
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else:
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return _InstanceEventsHold(target)
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return None
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@classmethod
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def _listen(cls, target, identifier, fn, raw=False, propagate=False):
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if not raw:
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orig_fn = fn
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def wrap(state, *arg, **kw):
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return orig_fn(state.obj(), *arg, **kw)
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fn = wrap
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event.Events._listen(target, identifier, fn, propagate=propagate)
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if propagate:
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for mgr in target.subclass_managers(True):
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event.Events._listen(mgr, identifier, fn, True)
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@classmethod
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def _remove(cls, identifier, target, fn):
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msg = "Removal of instance events not yet implemented"
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raise NotImplementedError(msg)
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@classmethod
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def _clear(cls):
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super(InstanceEvents, cls)._clear()
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_InstanceEventsHold._clear()
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def first_init(self, manager, cls):
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"""Called when the first instance of a particular mapping is called.
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"""
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def init(self, target, args, kwargs):
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"""Receive an instance when it's constructor is called.
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This method is only called during a userland construction of
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an object. It is not called when an object is loaded from the
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database.
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"""
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def init_failure(self, target, args, kwargs):
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"""Receive an instance when it's constructor has been called,
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and raised an exception.
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This method is only called during a userland construction of
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an object. It is not called when an object is loaded from the
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database.
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"""
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def load(self, target, context):
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"""Receive an object instance after it has been created via
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``__new__``, and after initial attribute population has
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occurred.
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This typically occurs when the instance is created based on
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incoming result rows, and is only called once for that
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instance's lifetime.
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Note that during a result-row load, this method is called upon
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the first row received for this instance. Note that some
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attributes and collections may or may not be loaded or even
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initialized, depending on what's present in the result rows.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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:param context: the :class:`.QueryContext` corresponding to the
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current :class:`.Query` in progress. This argument may be
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``None`` if the load does not correspond to a :class:`.Query`,
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such as during :meth:`.Session.merge`.
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"""
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def refresh(self, target, context, attrs):
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"""Receive an object instance after one or more attributes have
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been refreshed from a query.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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:param context: the :class:`.QueryContext` corresponding to the
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current :class:`.Query` in progress.
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:param attrs: iterable collection of attribute names which
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were populated, or None if all column-mapped, non-deferred
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attributes were populated.
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"""
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def expire(self, target, attrs):
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"""Receive an object instance after its attributes or some subset
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have been expired.
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'keys' is a list of attribute names. If None, the entire
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state was expired.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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:param attrs: iterable collection of attribute
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names which were expired, or None if all attributes were
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expired.
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"""
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def resurrect(self, target):
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"""Receive an object instance as it is 'resurrected' from
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garbage collection, which occurs when a "dirty" state falls
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out of scope.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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"""
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def pickle(self, target, state_dict):
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"""Receive an object instance when its associated state is
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being pickled.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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:param state_dict: the dictionary returned by
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:class:`.InstanceState.__getstate__`, containing the state
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to be pickled.
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"""
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def unpickle(self, target, state_dict):
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"""Receive an object instance after it's associated state has
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been unpickled.
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:param target: the mapped instance. If
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the event is configured with ``raw=True``, this will
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instead be the :class:`.InstanceState` state-management
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object associated with the instance.
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:param state_dict: the dictionary sent to
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:class:`.InstanceState.__setstate__`, containing the state
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dictionary which was pickled.
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"""
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class _EventsHold(object):
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"""Hold onto listeners against unmapped, uninstrumented classes.
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Establish _listen() for that class' mapper/instrumentation when
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those objects are created for that class.
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"""
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def __init__(self, class_):
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self.class_ = class_
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@classmethod
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def _clear(cls):
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cls.all_holds.clear()
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class HoldEvents(object):
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@classmethod
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def _listen(cls, target, identifier, fn, raw=False, propagate=False):
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if target.class_ in target.all_holds:
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collection = target.all_holds[target.class_]
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else:
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collection = target.all_holds[target.class_] = []
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collection.append((identifier, fn, raw, propagate))
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if propagate:
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stack = list(target.class_.__subclasses__())
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while stack:
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subclass = stack.pop(0)
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stack.extend(subclass.__subclasses__())
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subject = target.resolve(subclass)
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if subject is not None:
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subject.dispatch._listen(subject, identifier, fn,
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raw=raw, propagate=propagate)
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@classmethod
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def populate(cls, class_, subject):
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for subclass in class_.__mro__:
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if subclass in cls.all_holds:
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collection = cls.all_holds[subclass]
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for ident, fn, raw, propagate in collection:
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if propagate or subclass is class_:
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# since we can't be sure in what order different classes
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# in a hierarchy are triggered with populate(),
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# we rely upon _EventsHold for all event
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# assignment, instead of using the generic propagate
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# flag.
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subject.dispatch._listen(subject, ident,
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fn, raw=raw,
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propagate=False)
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class _InstanceEventsHold(_EventsHold):
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all_holds = weakref.WeakKeyDictionary()
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def resolve(self, class_):
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return orm.instrumentation.manager_of_class(class_)
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class HoldInstanceEvents(_EventsHold.HoldEvents, InstanceEvents):
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pass
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dispatch = event.dispatcher(HoldInstanceEvents)
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class MapperEvents(event.Events):
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"""Define events specific to mappings.
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e.g.::
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from sqlalchemy import event
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def my_before_insert_listener(mapper, connection, target):
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# execute a stored procedure upon INSERT,
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# apply the value to the row to be inserted
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target.calculated_value = connection.scalar(
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"select my_special_function(%d)"
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% target.special_number)
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# associate the listener function with SomeClass,
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# to execute during the "before_insert" hook
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event.listen(
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SomeClass, 'before_insert', my_before_insert_listener)
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Available targets include:
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* mapped classes
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* unmapped superclasses of mapped or to-be-mapped classes
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(using the ``propagate=True`` flag)
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* :class:`.Mapper` objects
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* the :class:`.Mapper` class itself and the :func:`.mapper`
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function indicate listening for all mappers.
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.. versionchanged:: 0.8.0 mapper events can be associated with
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unmapped superclasses of mapped classes.
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Mapper events provide hooks into critical sections of the
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mapper, including those related to object instrumentation,
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object loading, and object persistence. In particular, the
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persistence methods :meth:`~.MapperEvents.before_insert`,
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and :meth:`~.MapperEvents.before_update` are popular
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places to augment the state being persisted - however, these
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methods operate with several significant restrictions. The
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user is encouraged to evaluate the
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:meth:`.SessionEvents.before_flush` and
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:meth:`.SessionEvents.after_flush` methods as more
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flexible and user-friendly hooks in which to apply
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additional database state during a flush.
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When using :class:`.MapperEvents`, several modifiers are
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available to the :func:`.event.listen` function.
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:param propagate=False: When True, the event listener should
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be applied to all inheriting mappers and/or the mappers of
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inheriting classes, as well as any
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mapper which is the target of this listener.
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:param raw=False: When True, the "target" argument passed
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to applicable event listener functions will be the
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instance's :class:`.InstanceState` management
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object, rather than the mapped instance itself.
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:param retval=False: when True, the user-defined event function
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must have a return value, the purpose of which is either to
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control subsequent event propagation, or to otherwise alter
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the operation in progress by the mapper. Possible return
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values are:
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* ``sqlalchemy.orm.interfaces.EXT_CONTINUE`` - continue event
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processing normally.
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* ``sqlalchemy.orm.interfaces.EXT_STOP`` - cancel all subsequent
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event handlers in the chain.
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* other values - the return value specified by specific listeners,
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such as :meth:`~.MapperEvents.translate_row` or
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:meth:`~.MapperEvents.create_instance`.
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"""
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@classmethod
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def _accept_with(cls, target):
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if target is orm.mapper:
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return orm.Mapper
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elif isinstance(target, type):
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if issubclass(target, orm.Mapper):
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return target
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else:
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mapper = orm.util._mapper_or_none(target)
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if mapper is not None:
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return mapper
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else:
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return _MapperEventsHold(target)
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else:
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return target
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@classmethod
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def _listen(cls, target, identifier, fn,
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raw=False, retval=False, propagate=False):
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if not raw or not retval:
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if not raw:
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meth = getattr(cls, identifier)
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try:
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target_index = \
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inspect.getargspec(meth)[0].index('target') - 1
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except ValueError:
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target_index = None
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wrapped_fn = fn
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def wrap(*arg, **kw):
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if not raw and target_index is not None:
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arg = list(arg)
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arg[target_index] = arg[target_index].obj()
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if not retval:
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wrapped_fn(*arg, **kw)
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return orm.interfaces.EXT_CONTINUE
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else:
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return wrapped_fn(*arg, **kw)
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fn = wrap
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if propagate:
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for mapper in target.self_and_descendants:
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event.Events._listen(mapper, identifier, fn, propagate=True)
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else:
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event.Events._listen(target, identifier, fn)
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@classmethod
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def _clear(cls):
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super(MapperEvents, cls)._clear()
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_MapperEventsHold._clear()
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def instrument_class(self, mapper, class_):
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"""Receive a class when the mapper is first constructed,
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before instrumentation is applied to the mapped class.
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This event is the earliest phase of mapper construction.
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Most attributes of the mapper are not yet initialized.
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This listener can either be applied to the :class:`.Mapper`
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class overall, or to any un-mapped class which serves as a base
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for classes that will be mapped (using the ``propagate=True`` flag)::
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Base = declarative_base()
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@event.listens_for(Base, "instrument_class", propagate=True)
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def on_new_class(mapper, cls_):
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" ... "
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:param mapper: the :class:`.Mapper` which is the target
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of this event.
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:param class\_: the mapped class.
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"""
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def mapper_configured(self, mapper, class_):
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"""Called when the mapper for the class is fully configured.
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This event is the latest phase of mapper construction, and
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is invoked when the mapped classes are first used, so that
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relationships between mappers can be resolved. When the event is
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called, the mapper should be in its final state.
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While the configuration event normally occurs automatically,
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it can be forced to occur ahead of time, in the case where the event
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is needed before any actual mapper usage, by using the
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:func:`.configure_mappers` function.
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|
|
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:param mapper: the :class:`.Mapper` which is the target
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of this event.
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:param class\_: the mapped class.
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"""
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# TODO: need coverage for this event
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|
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def after_configured(self):
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"""Called after a series of mappers have been configured.
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|
|
This corresponds to the :func:`.orm.configure_mappers` call, which
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note is usually called automatically as mappings are first
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used.
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|
|
Theoretically this event is called once per
|
|
application, but is actually called any time new mappers
|
|
have been affected by a :func:`.orm.configure_mappers`
|
|
call. If new mappings are constructed after existing ones have
|
|
already been used, this event can be called again.
|
|
|
|
"""
|
|
|
|
def translate_row(self, mapper, context, row):
|
|
"""Perform pre-processing on the given result row and return a
|
|
new row instance.
|
|
|
|
This listener is typically registered with ``retval=True``.
|
|
It is called when the mapper first receives a row, before
|
|
the object identity or the instance itself has been derived
|
|
from that row. The given row may or may not be a
|
|
:class:`.RowProxy` object - it will always be a dictionary-like
|
|
object which contains mapped columns as keys. The
|
|
returned object should also be a dictionary-like object
|
|
which recognizes mapped columns as keys.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param context: the :class:`.QueryContext`, which includes
|
|
a handle to the current :class:`.Query` in progress as well
|
|
as additional state information.
|
|
:param row: the result row being handled. This may be
|
|
an actual :class:`.RowProxy` or may be a dictionary containing
|
|
:class:`.Column` objects as keys.
|
|
:return: When configured with ``retval=True``, the function
|
|
should return a dictionary-like row object, or ``EXT_CONTINUE``,
|
|
indicating the original row should be used.
|
|
|
|
|
|
"""
|
|
|
|
def create_instance(self, mapper, context, row, class_):
|
|
"""Receive a row when a new object instance is about to be
|
|
created from that row.
|
|
|
|
The method can choose to create the instance itself, or it can return
|
|
EXT_CONTINUE to indicate normal object creation should take place.
|
|
This listener is typically registered with ``retval=True``.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param context: the :class:`.QueryContext`, which includes
|
|
a handle to the current :class:`.Query` in progress as well
|
|
as additional state information.
|
|
:param row: the result row being handled. This may be
|
|
an actual :class:`.RowProxy` or may be a dictionary containing
|
|
:class:`.Column` objects as keys.
|
|
:param class\_: the mapped class.
|
|
:return: When configured with ``retval=True``, the return value
|
|
should be a newly created instance of the mapped class,
|
|
or ``EXT_CONTINUE`` indicating that default object construction
|
|
should take place.
|
|
|
|
"""
|
|
|
|
def append_result(self, mapper, context, row, target,
|
|
result, **flags):
|
|
"""Receive an object instance before that instance is appended
|
|
to a result list.
|
|
|
|
This is a rarely used hook which can be used to alter
|
|
the construction of a result list returned by :class:`.Query`.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param context: the :class:`.QueryContext`, which includes
|
|
a handle to the current :class:`.Query` in progress as well
|
|
as additional state information.
|
|
:param row: the result row being handled. This may be
|
|
an actual :class:`.RowProxy` or may be a dictionary containing
|
|
:class:`.Column` objects as keys.
|
|
:param target: the mapped instance being populated. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:param result: a list-like object where results are being
|
|
appended.
|
|
:param \**flags: Additional state information about the
|
|
current handling of the row.
|
|
:return: If this method is registered with ``retval=True``,
|
|
a return value of ``EXT_STOP`` will prevent the instance
|
|
from being appended to the given result list, whereas a
|
|
return value of ``EXT_CONTINUE`` will result in the default
|
|
behavior of appending the value to the result list.
|
|
|
|
"""
|
|
|
|
def populate_instance(self, mapper, context, row,
|
|
target, **flags):
|
|
"""Receive an instance before that instance has
|
|
its attributes populated.
|
|
|
|
This usually corresponds to a newly loaded instance but may
|
|
also correspond to an already-loaded instance which has
|
|
unloaded attributes to be populated. The method may be called
|
|
many times for a single instance, as multiple result rows are
|
|
used to populate eagerly loaded collections.
|
|
|
|
Most usages of this hook are obsolete. For a
|
|
generic "object has been newly created from a row" hook, use
|
|
:meth:`.InstanceEvents.load`.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param context: the :class:`.QueryContext`, which includes
|
|
a handle to the current :class:`.Query` in progress as well
|
|
as additional state information.
|
|
:param row: the result row being handled. This may be
|
|
an actual :class:`.RowProxy` or may be a dictionary containing
|
|
:class:`.Column` objects as keys.
|
|
:param target: the mapped instance. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: When configured with ``retval=True``, a return
|
|
value of ``EXT_STOP`` will bypass instance population by
|
|
the mapper. A value of ``EXT_CONTINUE`` indicates that
|
|
default instance population should take place.
|
|
|
|
"""
|
|
|
|
def before_insert(self, mapper, connection, target):
|
|
"""Receive an object instance before an INSERT statement
|
|
is emitted corresponding to that instance.
|
|
|
|
This event is used to modify local, non-object related
|
|
attributes on the instance before an INSERT occurs, as well
|
|
as to emit additional SQL statements on the given
|
|
connection.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class before their INSERT statements are emitted at
|
|
once in a later step. In the extremely rare case that
|
|
this is not desirable, the :func:`.mapper` can be
|
|
configured with ``batch=False``, which will cause
|
|
batches of instances to be broken up into individual
|
|
(and more poorly performing) event->persist->event
|
|
steps.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given**
|
|
:class:`.Connection` **only.** Handlers here should **not** make
|
|
alterations to the state of the :class:`.Session` overall, and
|
|
in general should not affect any :func:`.relationship` -mapped
|
|
attributes, as session cascade rules will not function properly,
|
|
nor is it always known if the related class has already been
|
|
handled. Operations that **are not supported in mapper
|
|
events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself, or
|
|
another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit INSERT statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being persisted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
|
|
"""
|
|
|
|
def after_insert(self, mapper, connection, target):
|
|
"""Receive an object instance after an INSERT statement
|
|
is emitted corresponding to that instance.
|
|
|
|
This event is used to modify in-Python-only
|
|
state on the instance after an INSERT occurs, as well
|
|
as to emit additional SQL statements on the given
|
|
connection.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class after their INSERT statements have been
|
|
emitted at once in a previous step. In the extremely
|
|
rare case that this is not desirable, the
|
|
:func:`.mapper` can be configured with ``batch=False``,
|
|
which will cause batches of instances to be broken up
|
|
into individual (and more poorly performing)
|
|
event->persist->event steps.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given**
|
|
:class:`.Connection` **only.** Handlers here should **not** make
|
|
alterations to the state of the :class:`.Session` overall, and in
|
|
general should not affect any :func:`.relationship` -mapped
|
|
attributes, as session cascade rules will not function properly,
|
|
nor is it always known if the related class has already been
|
|
handled. Operations that **are not supported in mapper
|
|
events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself,
|
|
or another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit INSERT statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being persisted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
|
|
"""
|
|
|
|
def before_update(self, mapper, connection, target):
|
|
"""Receive an object instance before an UPDATE statement
|
|
is emitted corresponding to that instance.
|
|
|
|
This event is used to modify local, non-object related
|
|
attributes on the instance before an UPDATE occurs, as well
|
|
as to emit additional SQL statements on the given
|
|
connection.
|
|
|
|
This method is called for all instances that are
|
|
marked as "dirty", *even those which have no net changes
|
|
to their column-based attributes*. An object is marked
|
|
as dirty when any of its column-based attributes have a
|
|
"set attribute" operation called or when any of its
|
|
collections are modified. If, at update time, no
|
|
column-based attributes have any net changes, no UPDATE
|
|
statement will be issued. This means that an instance
|
|
being sent to :meth:`~.MapperEvents.before_update` is
|
|
*not* a guarantee that an UPDATE statement will be
|
|
issued, although you can affect the outcome here by
|
|
modifying attributes so that a net change in value does
|
|
exist.
|
|
|
|
To detect if the column-based attributes on the object have net
|
|
changes, and will therefore generate an UPDATE statement, use
|
|
``object_session(instance).is_modified(instance,
|
|
include_collections=False)``.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class before their UPDATE statements are emitted at
|
|
once in a later step. In the extremely rare case that
|
|
this is not desirable, the :func:`.mapper` can be
|
|
configured with ``batch=False``, which will cause
|
|
batches of instances to be broken up into individual
|
|
(and more poorly performing) event->persist->event
|
|
steps.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given** :class:`.Connection`
|
|
**only.** Handlers here should **not** make alterations to the
|
|
state of the :class:`.Session` overall, and in general should not
|
|
affect any :func:`.relationship` -mapped attributes, as
|
|
session cascade rules will not function properly, nor is it
|
|
always known if the related class has already been handled.
|
|
Operations that **are not supported in mapper events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself,
|
|
or another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit UPDATE statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being persisted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
"""
|
|
|
|
def after_update(self, mapper, connection, target):
|
|
"""Receive an object instance after an UPDATE statement
|
|
is emitted corresponding to that instance.
|
|
|
|
This event is used to modify in-Python-only
|
|
state on the instance after an UPDATE occurs, as well
|
|
as to emit additional SQL statements on the given
|
|
connection.
|
|
|
|
This method is called for all instances that are
|
|
marked as "dirty", *even those which have no net changes
|
|
to their column-based attributes*, and for which
|
|
no UPDATE statement has proceeded. An object is marked
|
|
as dirty when any of its column-based attributes have a
|
|
"set attribute" operation called or when any of its
|
|
collections are modified. If, at update time, no
|
|
column-based attributes have any net changes, no UPDATE
|
|
statement will be issued. This means that an instance
|
|
being sent to :meth:`~.MapperEvents.after_update` is
|
|
*not* a guarantee that an UPDATE statement has been
|
|
issued.
|
|
|
|
To detect if the column-based attributes on the object have net
|
|
changes, and therefore resulted in an UPDATE statement, use
|
|
``object_session(instance).is_modified(instance,
|
|
include_collections=False)``.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class after their UPDATE statements have been emitted at
|
|
once in a previous step. In the extremely rare case that
|
|
this is not desirable, the :func:`.mapper` can be
|
|
configured with ``batch=False``, which will cause
|
|
batches of instances to be broken up into individual
|
|
(and more poorly performing) event->persist->event
|
|
steps.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given** :class:`.Connection`
|
|
**only.** Handlers here should **not** make alterations to the
|
|
state of the :class:`.Session` overall, and in general should not
|
|
affect any :func:`.relationship` -mapped attributes, as
|
|
session cascade rules will not function properly, nor is it
|
|
always known if the related class has already been handled.
|
|
Operations that **are not supported in mapper events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself,
|
|
or another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit UPDATE statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being persisted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
|
|
"""
|
|
|
|
def before_delete(self, mapper, connection, target):
|
|
"""Receive an object instance before a DELETE statement
|
|
is emitted corresponding to that instance.
|
|
|
|
This event is used to emit additional SQL statements on
|
|
the given connection as well as to perform application
|
|
specific bookkeeping related to a deletion event.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class before their DELETE statements are emitted at
|
|
once in a later step.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given** :class:`.Connection`
|
|
**only.** Handlers here should **not** make alterations to the
|
|
state of the :class:`.Session` overall, and in general should not
|
|
affect any :func:`.relationship` -mapped attributes, as
|
|
session cascade rules will not function properly, nor is it
|
|
always known if the related class has already been handled.
|
|
Operations that **are not supported in mapper events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself,
|
|
or another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit DELETE statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being deleted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
|
|
"""
|
|
|
|
def after_delete(self, mapper, connection, target):
|
|
"""Receive an object instance after a DELETE statement
|
|
has been emitted corresponding to that instance.
|
|
|
|
This event is used to emit additional SQL statements on
|
|
the given connection as well as to perform application
|
|
specific bookkeeping related to a deletion event.
|
|
|
|
The event is often called for a batch of objects of the
|
|
same class after their DELETE statements have been emitted at
|
|
once in a previous step.
|
|
|
|
.. warning::
|
|
Mapper-level flush events are designed to operate **on attributes
|
|
local to the immediate object being handled
|
|
and via SQL operations with the given** :class:`.Connection`
|
|
**only.** Handlers here should **not** make alterations to the
|
|
state of the :class:`.Session` overall, and in general should not
|
|
affect any :func:`.relationship` -mapped attributes, as
|
|
session cascade rules will not function properly, nor is it
|
|
always known if the related class has already been handled.
|
|
Operations that **are not supported in mapper events** include:
|
|
|
|
* :meth:`.Session.add`
|
|
* :meth:`.Session.delete`
|
|
* Mapped collection append, add, remove, delete, discard, etc.
|
|
* Mapped relationship attribute set/del events,
|
|
i.e. ``someobject.related = someotherobject``
|
|
|
|
Operations which manipulate the state of the object
|
|
relative to other objects are better handled:
|
|
|
|
* In the ``__init__()`` method of the mapped object itself,
|
|
or another method designed to establish some particular state.
|
|
* In a ``@validates`` handler, see :ref:`simple_validators`
|
|
* Within the :meth:`.SessionEvents.before_flush` event.
|
|
|
|
:param mapper: the :class:`.Mapper` which is the target
|
|
of this event.
|
|
:param connection: the :class:`.Connection` being used to
|
|
emit DELETE statements for this instance. This
|
|
provides a handle into the current transaction on the
|
|
target database specific to this instance.
|
|
:param target: the mapped instance being deleted. If
|
|
the event is configured with ``raw=True``, this will
|
|
instead be the :class:`.InstanceState` state-management
|
|
object associated with the instance.
|
|
:return: No return value is supported by this event.
|
|
|
|
"""
|
|
|
|
@classmethod
|
|
def _remove(cls, identifier, target, fn):
|
|
"Removal of mapper events not yet implemented"
|
|
raise NotImplementedError(msg)
|
|
|
|
|
|
class _MapperEventsHold(_EventsHold):
|
|
all_holds = weakref.WeakKeyDictionary()
|
|
|
|
def resolve(self, class_):
|
|
return orm.util._mapper_or_none(class_)
|
|
|
|
class HoldMapperEvents(_EventsHold.HoldEvents, MapperEvents):
|
|
pass
|
|
|
|
dispatch = event.dispatcher(HoldMapperEvents)
|
|
|
|
|
|
class SessionEvents(event.Events):
|
|
"""Define events specific to :class:`.Session` lifecycle.
|
|
|
|
e.g.::
|
|
|
|
from sqlalchemy import event
|
|
from sqlalchemy.orm import sessionmaker
|
|
|
|
def my_before_commit(session):
|
|
print "before commit!"
|
|
|
|
Session = sessionmaker()
|
|
|
|
event.listen(Session, "before_commit", my_before_commit)
|
|
|
|
The :func:`~.event.listen` function will accept
|
|
:class:`.Session` objects as well as the return result
|
|
of :func:`.sessionmaker` and :func:`.scoped_session`.
|
|
|
|
Additionally, it accepts the :class:`.Session` class which
|
|
will apply listeners to all :class:`.Session` instances
|
|
globally.
|
|
|
|
"""
|
|
@classmethod
|
|
def _accept_with(cls, target):
|
|
if isinstance(target, orm.scoped_session):
|
|
|
|
target = target.session_factory
|
|
if not isinstance(target, orm.sessionmaker) and \
|
|
(
|
|
not isinstance(target, type) or
|
|
not issubclass(target, orm.Session)
|
|
):
|
|
raise exc.ArgumentError(
|
|
"Session event listen on a scoped_session "
|
|
"requires that its creation callable "
|
|
"is associated with the Session class.")
|
|
|
|
if isinstance(target, orm.sessionmaker):
|
|
return target.class_
|
|
elif isinstance(target, type):
|
|
if issubclass(target, orm.scoped_session):
|
|
return orm.Session
|
|
elif issubclass(target, orm.Session):
|
|
return target
|
|
elif isinstance(target, orm.Session):
|
|
return target
|
|
else:
|
|
return None
|
|
|
|
@classmethod
|
|
def _remove(cls, identifier, target, fn):
|
|
msg = "Removal of session events not yet implemented"
|
|
raise NotImplementedError(msg)
|
|
|
|
def after_transaction_create(self, session, transaction):
|
|
"""Execute when a new :class:`.SessionTransaction` is created.
|
|
|
|
This event differs from :meth:`~.SessionEvents.after_begin`
|
|
in that it occurs for each :class:`.SessionTransaction`
|
|
overall, as opposed to when transactions are begun
|
|
on individual database connections. It is also invoked
|
|
for nested transactions and subtransactions, and is always
|
|
matched by a corresponding
|
|
:meth:`~.SessionEvents.after_transaction_end` event
|
|
(assuming normal operation of the :class:`.Session`).
|
|
|
|
:param session: the target :class:`.Session`.
|
|
:param transaction: the target :class:`.SessionTransaction`.
|
|
|
|
.. versionadded:: 0.8
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.after_transaction_end`
|
|
|
|
"""
|
|
|
|
def after_transaction_end(self, session, transaction):
|
|
"""Execute when the span of a :class:`.SessionTransaction` ends.
|
|
|
|
This event differs from :meth:`~.SessionEvents.after_commit`
|
|
in that it corresponds to all :class:`.SessionTransaction`
|
|
objects in use, including those for nested transactions
|
|
and subtransactions, and is always matched by a corresponding
|
|
:meth:`~.SessionEvents.after_transaction_create` event.
|
|
|
|
:param session: the target :class:`.Session`.
|
|
:param transaction: the target :class:`.SessionTransaction`.
|
|
|
|
.. versionadded:: 0.8
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.after_transaction_create`
|
|
|
|
"""
|
|
|
|
def before_commit(self, session):
|
|
"""Execute before commit is called.
|
|
|
|
.. note::
|
|
|
|
The :meth:`.before_commit` hook is *not* per-flush,
|
|
that is, the :class:`.Session` can emit SQL to the database
|
|
many times within the scope of a transaction.
|
|
For interception of these events, use the :meth:`~.SessionEvents.before_flush`,
|
|
:meth:`~.SessionEvents.after_flush`, or :meth:`~.SessionEvents.after_flush_postexec`
|
|
events.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.after_commit`
|
|
|
|
:meth:`~.SessionEvents.after_begin`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_create`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_end`
|
|
|
|
"""
|
|
|
|
def after_commit(self, session):
|
|
"""Execute after a commit has occurred.
|
|
|
|
.. note::
|
|
|
|
The :meth:`~.SessionEvents.after_commit` hook is *not* per-flush,
|
|
that is, the :class:`.Session` can emit SQL to the database
|
|
many times within the scope of a transaction.
|
|
For interception of these events, use the :meth:`~.SessionEvents.before_flush`,
|
|
:meth:`~.SessionEvents.after_flush`, or :meth:`~.SessionEvents.after_flush_postexec`
|
|
events.
|
|
|
|
.. note::
|
|
|
|
The :class:`.Session` is not in an active tranasction
|
|
when the :meth:`~.SessionEvents.after_commit` event is invoked, and therefore
|
|
can not emit SQL. To emit SQL corresponding to every transaction,
|
|
use the :meth:`~.SessionEvents.before_commit` event.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.before_commit`
|
|
|
|
:meth:`~.SessionEvents.after_begin`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_create`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_end`
|
|
|
|
"""
|
|
|
|
def after_rollback(self, session):
|
|
"""Execute after a real DBAPI rollback has occurred.
|
|
|
|
Note that this event only fires when the *actual* rollback against
|
|
the database occurs - it does *not* fire each time the
|
|
:meth:`.Session.rollback` method is called, if the underlying
|
|
DBAPI transaction has already been rolled back. In many
|
|
cases, the :class:`.Session` will not be in
|
|
an "active" state during this event, as the current
|
|
transaction is not valid. To acquire a :class:`.Session`
|
|
which is active after the outermost rollback has proceeded,
|
|
use the :meth:`.SessionEvents.after_soft_rollback` event, checking the
|
|
:attr:`.Session.is_active` flag.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
|
|
"""
|
|
|
|
def after_soft_rollback(self, session, previous_transaction):
|
|
"""Execute after any rollback has occurred, including "soft"
|
|
rollbacks that don't actually emit at the DBAPI level.
|
|
|
|
This corresponds to both nested and outer rollbacks, i.e.
|
|
the innermost rollback that calls the DBAPI's
|
|
rollback() method, as well as the enclosing rollback
|
|
calls that only pop themselves from the transaction stack.
|
|
|
|
The given :class:`.Session` can be used to invoke SQL and
|
|
:meth:`.Session.query` operations after an outermost rollback
|
|
by first checking the :attr:`.Session.is_active` flag::
|
|
|
|
@event.listens_for(Session, "after_soft_rollback")
|
|
def do_something(session, previous_transaction):
|
|
if session.is_active:
|
|
session.execute("select * from some_table")
|
|
|
|
:param session: The target :class:`.Session`.
|
|
:param previous_transaction: The :class:`.SessionTransaction`
|
|
transactional marker object which was just closed. The current
|
|
:class:`.SessionTransaction` for the given :class:`.Session` is
|
|
available via the :attr:`.Session.transaction` attribute.
|
|
|
|
.. versionadded:: 0.7.3
|
|
|
|
"""
|
|
|
|
def before_flush(self, session, flush_context, instances):
|
|
"""Execute before flush process has started.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
:param flush_context: Internal :class:`.UOWTransaction` object
|
|
which handles the details of the flush.
|
|
:param instances: Usually ``None``, this is the collection of
|
|
objects which can be passed to the :meth:`.Session.flush` method
|
|
(note this usage is deprecated).
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.after_flush`
|
|
|
|
:meth:`~.SessionEvents.after_flush_postexec`
|
|
|
|
"""
|
|
|
|
def after_flush(self, session, flush_context):
|
|
"""Execute after flush has completed, but before commit has been
|
|
called.
|
|
|
|
Note that the session's state is still in pre-flush, i.e. 'new',
|
|
'dirty', and 'deleted' lists still show pre-flush state as well
|
|
as the history settings on instance attributes.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
:param flush_context: Internal :class:`.UOWTransaction` object
|
|
which handles the details of the flush.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.before_flush`
|
|
|
|
:meth:`~.SessionEvents.after_flush_postexec`
|
|
|
|
"""
|
|
|
|
def after_flush_postexec(self, session, flush_context):
|
|
"""Execute after flush has completed, and after the post-exec
|
|
state occurs.
|
|
|
|
This will be when the 'new', 'dirty', and 'deleted' lists are in
|
|
their final state. An actual commit() may or may not have
|
|
occurred, depending on whether or not the flush started its own
|
|
transaction or participated in a larger transaction.
|
|
|
|
:param session: The target :class:`.Session`.
|
|
:param flush_context: Internal :class:`.UOWTransaction` object
|
|
which handles the details of the flush.
|
|
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.before_flush`
|
|
|
|
:meth:`~.SessionEvents.after_flush`
|
|
|
|
"""
|
|
|
|
def after_begin(self, session, transaction, connection):
|
|
"""Execute after a transaction is begun on a connection
|
|
|
|
:param session: The target :class:`.Session`.
|
|
:param transaction: The :class:`.SessionTransaction`.
|
|
:param connection: The :class:`~.engine.Connection` object
|
|
which will be used for SQL statements.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.before_commit`
|
|
|
|
:meth:`~.SessionEvents.after_commit`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_create`
|
|
|
|
:meth:`~.SessionEvents.after_transaction_end`
|
|
|
|
"""
|
|
|
|
def before_attach(self, session, instance):
|
|
"""Execute before an instance is attached to a session.
|
|
|
|
This is called before an add, delete or merge causes
|
|
the object to be part of the session.
|
|
|
|
.. versionadded:: 0.8. Note that :meth:`.after_attach` now
|
|
fires off after the item is part of the session.
|
|
:meth:`.before_attach` is provided for those cases where
|
|
the item should not yet be part of the session state.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.after_attach`
|
|
|
|
"""
|
|
|
|
def after_attach(self, session, instance):
|
|
"""Execute after an instance is attached to a session.
|
|
|
|
This is called after an add, delete or merge.
|
|
|
|
.. note::
|
|
|
|
As of 0.8, this event fires off *after* the item
|
|
has been fully associated with the session, which is
|
|
different than previous releases. For event
|
|
handlers that require the object not yet
|
|
be part of session state (such as handlers which
|
|
may autoflush while the target object is not
|
|
yet complete) consider the
|
|
new :meth:`.before_attach` event.
|
|
|
|
.. seealso::
|
|
|
|
:meth:`~.SessionEvents.before_attach`
|
|
|
|
"""
|
|
|
|
def after_bulk_update(self, session, query, query_context, result):
|
|
"""Execute after a bulk update operation to the session.
|
|
|
|
This is called as a result of the :meth:`.Query.update` method.
|
|
|
|
:param query: the :class:`.Query` object that this update operation was
|
|
called upon.
|
|
:param query_context: The :class:`.QueryContext` object, corresponding
|
|
to the invocation of an ORM query.
|
|
:param result: the :class:`.ResultProxy` returned as a result of the
|
|
bulk UPDATE operation.
|
|
|
|
"""
|
|
|
|
def after_bulk_delete(self, session, query, query_context, result):
|
|
"""Execute after a bulk delete operation to the session.
|
|
|
|
This is called as a result of the :meth:`.Query.delete` method.
|
|
|
|
:param query: the :class:`.Query` object that this update operation was
|
|
called upon.
|
|
:param query_context: The :class:`.QueryContext` object, corresponding
|
|
to the invocation of an ORM query.
|
|
:param result: the :class:`.ResultProxy` returned as a result of the
|
|
bulk DELETE operation.
|
|
|
|
"""
|
|
|
|
|
|
class AttributeEvents(event.Events):
|
|
"""Define events for object attributes.
|
|
|
|
These are typically defined on the class-bound descriptor for the
|
|
target class.
|
|
|
|
e.g.::
|
|
|
|
from sqlalchemy import event
|
|
|
|
def my_append_listener(target, value, initiator):
|
|
print "received append event for target: %s" % target
|
|
|
|
event.listen(MyClass.collection, 'append', my_append_listener)
|
|
|
|
Listeners have the option to return a possibly modified version
|
|
of the value, when the ``retval=True`` flag is passed
|
|
to :func:`~.event.listen`::
|
|
|
|
def validate_phone(target, value, oldvalue, initiator):
|
|
"Strip non-numeric characters from a phone number"
|
|
|
|
return re.sub(r'(?![0-9])', '', value)
|
|
|
|
# setup listener on UserContact.phone attribute, instructing
|
|
# it to use the return value
|
|
listen(UserContact.phone, 'set', validate_phone, retval=True)
|
|
|
|
A validation function like the above can also raise an exception
|
|
such as :class:`.ValueError` to halt the operation.
|
|
|
|
Several modifiers are available to the :func:`~.event.listen` function.
|
|
|
|
:param active_history=False: When True, indicates that the
|
|
"set" event would like to receive the "old" value being
|
|
replaced unconditionally, even if this requires firing off
|
|
database loads. Note that ``active_history`` can also be
|
|
set directly via :func:`.column_property` and
|
|
:func:`.relationship`.
|
|
|
|
:param propagate=False: When True, the listener function will
|
|
be established not just for the class attribute given, but
|
|
for attributes of the same name on all current subclasses
|
|
of that class, as well as all future subclasses of that
|
|
class, using an additional listener that listens for
|
|
instrumentation events.
|
|
:param raw=False: When True, the "target" argument to the
|
|
event will be the :class:`.InstanceState` management
|
|
object, rather than the mapped instance itself.
|
|
:param retval=False: when True, the user-defined event
|
|
listening must return the "value" argument from the
|
|
function. This gives the listening function the opportunity
|
|
to change the value that is ultimately used for a "set"
|
|
or "append" event.
|
|
|
|
"""
|
|
|
|
@classmethod
|
|
def _accept_with(cls, target):
|
|
# TODO: coverage
|
|
if isinstance(target, orm.interfaces.MapperProperty):
|
|
return getattr(target.parent.class_, target.key)
|
|
else:
|
|
return target
|
|
|
|
@classmethod
|
|
def _listen(cls, target, identifier, fn, active_history=False,
|
|
raw=False, retval=False,
|
|
propagate=False):
|
|
if active_history:
|
|
target.dispatch._active_history = True
|
|
|
|
# TODO: for removal, need to package the identity
|
|
# of the wrapper with the original function.
|
|
|
|
if not raw or not retval:
|
|
orig_fn = fn
|
|
|
|
def wrap(target, value, *arg):
|
|
if not raw:
|
|
target = target.obj()
|
|
if not retval:
|
|
orig_fn(target, value, *arg)
|
|
return value
|
|
else:
|
|
return orig_fn(target, value, *arg)
|
|
fn = wrap
|
|
|
|
event.Events._listen(target, identifier, fn, propagate)
|
|
|
|
if propagate:
|
|
manager = orm.instrumentation.manager_of_class(target.class_)
|
|
|
|
for mgr in manager.subclass_managers(True):
|
|
event.Events._listen(mgr[target.key], identifier, fn, True)
|
|
|
|
@classmethod
|
|
def _remove(cls, identifier, target, fn):
|
|
msg = "Removal of attribute events not yet implemented"
|
|
raise NotImplementedError(msg)
|
|
|
|
def append(self, target, value, initiator):
|
|
"""Receive a collection append event.
|
|
|
|
:param target: the object instance receiving the event.
|
|
If the listener is registered with ``raw=True``, this will
|
|
be the :class:`.InstanceState` object.
|
|
:param value: the value being appended. If this listener
|
|
is registered with ``retval=True``, the listener
|
|
function must return this value, or a new value which
|
|
replaces it.
|
|
:param initiator: the attribute implementation object
|
|
which initiated this event.
|
|
:return: if the event was registered with ``retval=True``,
|
|
the given value, or a new effective value, should be returned.
|
|
|
|
"""
|
|
|
|
def remove(self, target, value, initiator):
|
|
"""Receive a collection remove event.
|
|
|
|
:param target: the object instance receiving the event.
|
|
If the listener is registered with ``raw=True``, this will
|
|
be the :class:`.InstanceState` object.
|
|
:param value: the value being removed.
|
|
:param initiator: the attribute implementation object
|
|
which initiated this event.
|
|
:return: No return value is defined for this event.
|
|
"""
|
|
|
|
def set(self, target, value, oldvalue, initiator):
|
|
"""Receive a scalar set event.
|
|
|
|
:param target: the object instance receiving the event.
|
|
If the listener is registered with ``raw=True``, this will
|
|
be the :class:`.InstanceState` object.
|
|
:param value: the value being set. If this listener
|
|
is registered with ``retval=True``, the listener
|
|
function must return this value, or a new value which
|
|
replaces it.
|
|
:param oldvalue: the previous value being replaced. This
|
|
may also be the symbol ``NEVER_SET`` or ``NO_VALUE``.
|
|
If the listener is registered with ``active_history=True``,
|
|
the previous value of the attribute will be loaded from
|
|
the database if the existing value is currently unloaded
|
|
or expired.
|
|
:param initiator: the attribute implementation object
|
|
which initiated this event.
|
|
:return: if the event was registered with ``retval=True``,
|
|
the given value, or a new effective value, should be returned.
|
|
|
|
"""
|