text: # orm/instrumentation.py
  # Copyright (C) 2005-2012 the SQLAlchemy authors and contributors <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  """Defines SQLAlchemy's system of class instrumentation.
  
  This module is usually not directly visible to user applications, but
  defines a large part of the ORM's interactivity.
  
  instrumentation.py deals with registration of end-user classes
  for state tracking.   It interacts closely with state.py
  and attributes.py which establish per-instance and per-class-attribute
  instrumentation, respectively.
  
  SQLA's instrumentation system is completely customizable, in which
  case an understanding of the general mechanics of this module is helpful.
  An example of full customization is in /examples/custom_attributes.
  
  """
  
  
  from sqlalchemy.orm import exc, collections, events
  from operator import attrgetter, itemgetter
  from sqlalchemy import event, util
  import weakref
  from sqlalchemy.orm import state, attributes
  
  
  INSTRUMENTATION_MANAGER = '__sa_instrumentation_manager__'
  """Attribute, elects custom instrumentation when present on a mapped class.
  
  Allows a class to specify a slightly or wildly different technique for
  tracking changes made to mapped attributes and collections.
  
  Only one instrumentation implementation is allowed in a given object
  inheritance hierarchy.
  
  The value of this attribute must be a callable and will be passed a class
  object.  The callable must return one of:
  
    - An instance of an interfaces.InstrumentationManager or subclass
    - An object implementing all or some of InstrumentationManager (TODO)
    - A dictionary of callables, implementing all or some of the above (TODO)
    - An instance of a ClassManager or subclass
  
  interfaces.InstrumentationManager is public API and will remain stable
  between releases.  ClassManager is not public and no guarantees are made
  about stability.  Caveat emptor.
  
  This attribute is consulted by the default SQLAlchemy instrumentation
  resolution code.  If custom finders are installed in the global
  instrumentation_finders list, they may or may not choose to honor this
  attribute.
  
  """
  
  instrumentation_finders = []
  """An extensible sequence of instrumentation implementation finding callables.
  
  Finders callables will be passed a class object.  If None is returned, the
  next finder in the sequence is consulted.  Otherwise the return must be an
  instrumentation factory that follows the same guidelines as
  INSTRUMENTATION_MANAGER.
  
  By default, the only finder is find_native_user_instrumentation_hook, which
  searches for INSTRUMENTATION_MANAGER.  If all finders return None, standard
  ClassManager instrumentation is used.
  
  """
  
  
  class ClassManager(dict):
      """tracks state information at the class level."""
  
      MANAGER_ATTR = '_sa_class_manager'
      STATE_ATTR = '_sa_instance_state'
  
      deferred_scalar_loader = None
  
      original_init = object.__init__
  
      def __init__(self, class_):
          self.class_ = class_
          self.factory = None  # where we came from, for inheritance bookkeeping
          self.info = {}
          self.new_init = None
          self.mutable_attributes = set()
          self.local_attrs = {}
          self.originals = {}
  
          self._bases = [mgr for mgr in [
                          manager_of_class(base)
                          for base in self.class_.__bases__
                          if isinstance(base, type)
                   ] if mgr is not None]
  
          for base in self._bases:
              self.update(base)
  
          self.manage()
          self._instrument_init()
  
      dispatch = event.dispatcher(events.InstanceEvents)
  
      @property
      def is_mapped(self):
          return 'mapper' in self.__dict__
  
      @util.memoized_property
      def mapper(self):
          # raises unless self.mapper has been assigned
          raise exc.UnmappedClassError(self.class_)
  
      def _attr_has_impl(self, key):
          """Return True if the given attribute is fully initialized.
  
          i.e. has an impl.
          """
  
          return key in self and self[key].impl is not None
  
      def _subclass_manager(self, cls):
          """Create a new ClassManager for a subclass of this ClassManager's
          class.
  
          This is called automatically when attributes are instrumented so that
          the attributes can be propagated to subclasses against their own
          class-local manager, without the need for mappers etc. to have already
          pre-configured managers for the full class hierarchy.   Mappers
          can post-configure the auto-generated ClassManager when needed.
  
          """
          manager = manager_of_class(cls)
          if manager is None:
              manager = _create_manager_for_cls(cls, _source=self)
          return manager
  
      def _instrument_init(self):
          # TODO: self.class_.__init__ is often the already-instrumented
          # __init__ from an instrumented superclass.  We still need to make
          # our own wrapper, but it would
          # be nice to wrap the original __init__ and not our existing wrapper
          # of such, since this adds method overhead.
          self.original_init = self.class_.__init__
          self.new_init = _generate_init(self.class_, self)
          self.install_member('__init__', self.new_init)
  
      def _uninstrument_init(self):
          if self.new_init:
              self.uninstall_member('__init__')
              self.new_init = None
  
      @util.memoized_property
      def _state_constructor(self):
          self.dispatch.first_init(self, self.class_)
          if self.mutable_attributes:
              return state.MutableAttrInstanceState
          else:
              return state.InstanceState
  
      def manage(self):
          """Mark this instance as the manager for its class."""
  
          setattr(self.class_, self.MANAGER_ATTR, self)
  
      def dispose(self):
          """Dissasociate this manager from its class."""
  
          delattr(self.class_, self.MANAGER_ATTR)
  
      def manager_getter(self):
          return attrgetter(self.MANAGER_ATTR)
  
      def instrument_attribute(self, key, inst, propagated=False):
          if propagated:
              if key in self.local_attrs:
                  return  # don't override local attr with inherited attr
          else:
              self.local_attrs[key] = inst
              self.install_descriptor(key, inst)
          self[key] = inst
  
          for cls in self.class_.__subclasses__():
              manager = self._subclass_manager(cls)
              manager.instrument_attribute(key, inst, True)
  
      def subclass_managers(self, recursive):
          for cls in self.class_.__subclasses__():
              mgr = manager_of_class(cls)
              if mgr is not None and mgr is not self:
                  yield mgr
                  if recursive:
                      for m in mgr.subclass_managers(True):
                          yield m
  
      def post_configure_attribute(self, key):
          instrumentation_registry.dispatch.\
                  attribute_instrument(self.class_, key, self[key])
  
      def uninstrument_attribute(self, key, propagated=False):
          if key not in self:
              return
          if propagated:
              if key in self.local_attrs:
                  return  # don't get rid of local attr
          else:
              del self.local_attrs[key]
              self.uninstall_descriptor(key)
          del self[key]
          if key in self.mutable_attributes:
              self.mutable_attributes.remove(key)
          for cls in self.class_.__subclasses__():
              manager = manager_of_class(cls)
              if manager:
                  manager.uninstrument_attribute(key, True)
  
      def unregister(self):
          """remove all instrumentation established by this ClassManager."""
  
          self._uninstrument_init()
  
          self.mapper = self.dispatch = None
          self.info.clear()
  
          for key in list(self):
              if key in self.local_attrs:
                  self.uninstrument_attribute(key)
  
      def install_descriptor(self, key, inst):
          if key in (self.STATE_ATTR, self.MANAGER_ATTR):
              raise KeyError("%r: requested attribute name conflicts with "
                             "instrumentation attribute of the same name." %
                             key)
          setattr(self.class_, key, inst)
  
      def uninstall_descriptor(self, key):
          delattr(self.class_, key)
  
      def install_member(self, key, implementation):
          if key in (self.STATE_ATTR, self.MANAGER_ATTR):
              raise KeyError("%r: requested attribute name conflicts with "
                             "instrumentation attribute of the same name." %
                             key)
          self.originals.setdefault(key, getattr(self.class_, key, None))
          setattr(self.class_, key, implementation)
  
      def uninstall_member(self, key):
          original = self.originals.pop(key, None)
          if original is not None:
              setattr(self.class_, key, original)
  
      def instrument_collection_class(self, key, collection_class):
          return collections.prepare_instrumentation(collection_class)
  
      def initialize_collection(self, key, state, factory):
          user_data = factory()
          adapter = collections.CollectionAdapter(
              self.get_impl(key), state, user_data)
          return adapter, user_data
  
      def is_instrumented(self, key, search=False):
          if search:
              return key in self
          else:
              return key in self.local_attrs
  
      def get_impl(self, key):
          return self[key].impl
  
      @property
      def attributes(self):
          return self.itervalues()
  
      ## InstanceState management
  
      def new_instance(self, state=None):
          instance = self.class_.__new__(self.class_)
          setattr(instance, self.STATE_ATTR,
                      state or self._state_constructor(instance, self))
          return instance
  
      def setup_instance(self, instance, state=None):
          setattr(instance, self.STATE_ATTR,
                      state or self._state_constructor(instance, self))
  
      def teardown_instance(self, instance):
          delattr(instance, self.STATE_ATTR)
  
      def _new_state_if_none(self, instance):
          """Install a default InstanceState if none is present.
  
          A private convenience method used by the __init__ decorator.
  
          """
          if hasattr(instance, self.STATE_ATTR):
              return False
          elif self.class_ is not instance.__class__ and \
                  self.is_mapped:
              # this will create a new ClassManager for the
              # subclass, without a mapper.  This is likely a
              # user error situation but allow the object
              # to be constructed, so that it is usable
              # in a non-ORM context at least.
              return self._subclass_manager(instance.__class__).\
                          _new_state_if_none(instance)
          else:
              state = self._state_constructor(instance, self)
              setattr(instance, self.STATE_ATTR, state)
              return state
  
      def state_getter(self):
          """Return a (instance) -> InstanceState callable.
  
          "state getter" callables should raise either KeyError or
          AttributeError if no InstanceState could be found for the
          instance.
          """
  
          return attrgetter(self.STATE_ATTR)
  
      def dict_getter(self):
          return attrgetter('__dict__')
  
      def has_state(self, instance):
          return hasattr(instance, self.STATE_ATTR)
  
      def has_parent(self, state, key, optimistic=False):
          """TODO"""
          return self.get_impl(key).hasparent(state, optimistic=optimistic)
  
      def __nonzero__(self):
          """All ClassManagers are non-zero regardless of attribute state."""
          return True
  
      def __repr__(self):
          return '<%s of %r at %x>' % (
              self.__class__.__name__, self.class_, id(self))
  
  class _ClassInstrumentationAdapter(ClassManager):
      """Adapts a user-defined InstrumentationManager to a ClassManager."""
  
      def __init__(self, class_, override, **kw):
          self._adapted = override
          self._get_state = self._adapted.state_getter(class_)
          self._get_dict = self._adapted.dict_getter(class_)
  
          ClassManager.__init__(self, class_, **kw)
  
      def manage(self):
          self._adapted.manage(self.class_, self)
  
      def dispose(self):
          self._adapted.dispose(self.class_)
  
      def manager_getter(self):
          return self._adapted.manager_getter(self.class_)
  
      def instrument_attribute(self, key, inst, propagated=False):
          ClassManager.instrument_attribute(self, key, inst, propagated)
          if not propagated:
              self._adapted.instrument_attribute(self.class_, key, inst)
  
      def post_configure_attribute(self, key):
          super(_ClassInstrumentationAdapter, self).post_configure_attribute(key)
          self._adapted.post_configure_attribute(self.class_, key, self[key])
  
      def install_descriptor(self, key, inst):
          self._adapted.install_descriptor(self.class_, key, inst)
  
      def uninstall_descriptor(self, key):
          self._adapted.uninstall_descriptor(self.class_, key)
  
      def install_member(self, key, implementation):
          self._adapted.install_member(self.class_, key, implementation)
  
      def uninstall_member(self, key):
          self._adapted.uninstall_member(self.class_, key)
  
      def instrument_collection_class(self, key, collection_class):
          return self._adapted.instrument_collection_class(
              self.class_, key, collection_class)
  
      def initialize_collection(self, key, state, factory):
          delegate = getattr(self._adapted, 'initialize_collection', None)
          if delegate:
              return delegate(key, state, factory)
          else:
              return ClassManager.initialize_collection(self, key,
                                                          state, factory)
  
      def new_instance(self, state=None):
          instance = self.class_.__new__(self.class_)
          self.setup_instance(instance, state)
          return instance
  
      def _new_state_if_none(self, instance):
          """Install a default InstanceState if none is present.
  
          A private convenience method used by the __init__ decorator.
          """
          if self.has_state(instance):
              return False
          else:
              return self.setup_instance(instance)
  
      def setup_instance(self, instance, state=None):
          self._adapted.initialize_instance_dict(self.class_, instance)
  
          if state is None:
              state = self._state_constructor(instance, self)
  
          # the given instance is assumed to have no state
          self._adapted.install_state(self.class_, instance, state)
          return state
  
      def teardown_instance(self, instance):
          self._adapted.remove_state(self.class_, instance)
  
      def has_state(self, instance):
          try:
              state = self._get_state(instance)
          except exc.NO_STATE:
              return False
          else:
              return True
  
      def state_getter(self):
          return self._get_state
  
      def dict_getter(self):
          return self._get_dict
  
  def register_class(class_, **kw):
      """Register class instrumentation.
  
      Returns the existing or newly created class manager.
      """
  
      manager = manager_of_class(class_)
      if manager is None:
          manager = _create_manager_for_cls(class_, **kw)
      return manager
  
  def unregister_class(class_):
      """Unregister class instrumentation."""
  
      instrumentation_registry.unregister(class_)
  
  
  def is_instrumented(instance, key):
      """Return True if the given attribute on the given instance is
      instrumented by the attributes package.
  
      This function may be used regardless of instrumentation
      applied directly to the class, i.e. no descriptors are required.
  
      """
      return manager_of_class(instance.__class__).\
                          is_instrumented(key, search=True)
  
  class InstrumentationRegistry(object):
      """Private instrumentation registration singleton.
  
      All classes are routed through this registry
      when first instrumented, however the InstrumentationRegistry
      is not actually needed unless custom ClassManagers are in use.
  
      """
  
      _manager_finders = weakref.WeakKeyDictionary()
      _state_finders = util.WeakIdentityMapping()
      _dict_finders = util.WeakIdentityMapping()
      _extended = False
  
      dispatch = event.dispatcher(events.InstrumentationEvents)
  
      def create_manager_for_cls(self, class_, **kw):
          assert class_ is not None
          assert manager_of_class(class_) is None
  
          for finder in instrumentation_finders:
              factory = finder(class_)
              if factory is not None:
                  break
          else:
              factory = ClassManager
  
          existing_factories = self._collect_management_factories_for(class_).\
                                  difference([factory])
          if existing_factories:
              raise TypeError(
                  "multiple instrumentation implementations specified "
                  "in %s inheritance hierarchy: %r" % (
                      class_.__name__, list(existing_factories)))
  
          manager = factory(class_)
          if not isinstance(manager, ClassManager):
              manager = _ClassInstrumentationAdapter(class_, manager)
  
          if factory != ClassManager and not self._extended:
              # somebody invoked a custom ClassManager.
              # reinstall global "getter" functions with the more
              # expensive ones.
              self._extended = True
              _install_lookup_strategy(self)
  
          manager.factory = factory
          self._manager_finders[class_] = manager.manager_getter()
          self._state_finders[class_] = manager.state_getter()
          self._dict_finders[class_] = manager.dict_getter()
  
          self.dispatch.class_instrument(class_)
  
          return manager
  
      def _collect_management_factories_for(self, cls):
          """Return a collection of factories in play or specified for a
          hierarchy.
  
          Traverses the entire inheritance graph of a cls and returns a
          collection of instrumentation factories for those classes. Factories
          are extracted from active ClassManagers, if available, otherwise
          instrumentation_finders is consulted.
  
          """
          hierarchy = util.class_hierarchy(cls)
          factories = set()
          for member in hierarchy:
              manager = manager_of_class(member)
              if manager is not None:
                  factories.add(manager.factory)
              else:
                  for finder in instrumentation_finders:
                      factory = finder(member)
                      if factory is not None:
                          break
                  else:
                      factory = None
                  factories.add(factory)
          factories.discard(None)
          return factories
  
      def manager_of_class(self, cls):
          # this is only called when alternate instrumentation
          # has been established
          if cls is None:
              return None
          try:
              finder = self._manager_finders[cls]
          except KeyError:
              return None
          else:
              return finder(cls)
  
      def state_of(self, instance):
          # this is only called when alternate instrumentation
          # has been established
          if instance is None:
              raise AttributeError("None has no persistent state.")
          try:
              return self._state_finders[instance.__class__](instance)
          except KeyError:
              raise AttributeError("%r is not instrumented" %
                                      instance.__class__)
  
      def dict_of(self, instance):
          # this is only called when alternate instrumentation
          # has been established
          if instance is None:
              raise AttributeError("None has no persistent state.")
          try:
              return self._dict_finders[instance.__class__](instance)
          except KeyError:
              raise AttributeError("%r is not instrumented" %
                                      instance.__class__)
  
      def unregister(self, class_):
          if class_ in self._manager_finders:
              manager = self.manager_of_class(class_)
              self.dispatch.class_uninstrument(class_)
              manager.unregister()
              manager.dispose()
              del self._manager_finders[class_]
              del self._state_finders[class_]
              del self._dict_finders[class_]
          if ClassManager.MANAGER_ATTR in class_.__dict__:
              delattr(class_, ClassManager.MANAGER_ATTR)
  
  instrumentation_registry = InstrumentationRegistry()
  
  
  def _install_lookup_strategy(implementation):
      """Replace global class/object management functions
      with either faster or more comprehensive implementations,
      based on whether or not extended class instrumentation
      has been detected.
  
      This function is called only by InstrumentationRegistry()
      and unit tests specific to this behavior.
  
      """
      global instance_state, instance_dict, manager_of_class
      if implementation is util.symbol('native'):
          instance_state = attrgetter(ClassManager.STATE_ATTR)
          instance_dict = attrgetter("__dict__")
          def manager_of_class(cls):
              return cls.__dict__.get(ClassManager.MANAGER_ATTR, None)
      else:
          instance_state = instrumentation_registry.state_of
          instance_dict = instrumentation_registry.dict_of
          manager_of_class = instrumentation_registry.manager_of_class
      attributes.instance_state = instance_state
      attributes.instance_dict = instance_dict
      attributes.manager_of_class = manager_of_class
  
  _create_manager_for_cls = instrumentation_registry.create_manager_for_cls
  
  # Install default "lookup" strategies.  These are basically
  # very fast attrgetters for key attributes.
  # When a custom ClassManager is installed, more expensive per-class
  # strategies are copied over these.
  _install_lookup_strategy(util.symbol('native'))
  
  
  def find_native_user_instrumentation_hook(cls):
      """Find user-specified instrumentation management for a class."""
      return getattr(cls, INSTRUMENTATION_MANAGER, None)
  instrumentation_finders.append(find_native_user_instrumentation_hook)
  
  def _generate_init(class_, class_manager):
      """Build an __init__ decorator that triggers ClassManager events."""
  
      # TODO: we should use the ClassManager's notion of the
      # original '__init__' method, once ClassManager is fixed
      # to always reference that.
      original__init__ = class_.__init__
      assert original__init__
  
      # Go through some effort here and don't change the user's __init__
      # calling signature, including the unlikely case that it has
      # a return value.
      # FIXME: need to juggle local names to avoid constructor argument
      # clashes.
      func_body = """\
  def __init__(%(apply_pos)s):
      new_state = class_manager._new_state_if_none(%(self_arg)s)
      if new_state:
          return new_state.initialize_instance(%(apply_kw)s)
      else:
          return original__init__(%(apply_kw)s)
  """
      func_vars = util.format_argspec_init(original__init__, grouped=False)
      func_text = func_body % func_vars
  
      # Py3K
      #func_defaults = getattr(original__init__, '__defaults__', None)
      #func_kw_defaults = getattr(original__init__, '__kwdefaults__', None)
      # Py2K
      func = getattr(original__init__, 'im_func', original__init__)
      func_defaults = getattr(func, 'func_defaults', None)
      # end Py2K
  
      env = locals().copy()
      exec func_text in env
      __init__ = env['__init__']
      __init__.__doc__ = original__init__.__doc__
      if func_defaults:
          __init__.func_defaults = func_defaults
      # Py3K
      #if func_kw_defaults:
      #    __init__.__kwdefaults__ = func_kw_defaults
      return __init__
  