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"""this example illustrates how to replace SQLAlchemy's class descriptors with
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This sort of thing is appropriate for integration with frameworks that
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redefine class behaviors in their own way, such that SQLA's default
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instrumentation is not compatible.
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The example illustrates redefinition of instrumentation at the class level as
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well as the collection level, and redefines the storage of the class to store
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state within "instance._goofy_dict" instead of "instance.__dict__". Note that
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the default collection implementations can be used with a custom attribute
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"""Illustrates customized class instrumentation, using
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the :mod:`sqlalchemy.ext.instrumentation` extension package.
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In this example, mapped classes are modified to
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store their state in a dictionary attached to an attribute
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named "_goofy_dict", instead of using __dict__.
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this example illustrates how to replace SQLAlchemy's class
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descriptors with a user-defined system.
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from sqlalchemy import create_engine, MetaData, Table, Column, Integer, Text,\
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from sqlalchemy.orm import mapper, relationship, Session,\
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InstrumentationManager
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from sqlalchemy.orm import mapper, relationship, Session
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from sqlalchemy.orm.attributes import set_attribute, get_attribute, \
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from sqlalchemy.orm.instrumentation import is_instrumented
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from sqlalchemy.orm.collections import collection_adapter
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from sqlalchemy.ext.instrumentation import InstrumentationManager
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class MyClassState(InstrumentationManager):
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def __init__(self, cls):
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def instrument_attribute(self, class_, key, attr):
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def install_descriptor(self, class_, key, attr):
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def uninstall_descriptor(self, class_, key, attr):
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def instrument_collection_class(self, class_, key, collection_class):
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def get_instance_dict(self, class_, instance):
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return instance._goofy_dict
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def initialize_instance_dict(self, class_, instance):
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instance.__dict__['_goofy_dict'] = {}
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def initialize_collection(self, key, state, factory):
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return MyCollectionAdapter(key, state, data), data
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def install_state(self, class_, instance, state):
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self.states[id(instance)] = state
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instance.__dict__['_goofy_dict']['state'] = state
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def state_getter(self, class_):
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def find(instance):
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return self.states[id(instance)]
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return instance.__dict__['_goofy_dict']['state']
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class MyClass(object):
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del self._goofy_dict[key]
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class MyCollectionAdapter(object):
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"""An wholly alternative instrumentation implementation."""
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def __init__(self, key, state, collection):
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self.collection = collection
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setattr(collection, '_sa_adapter', self)
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def unlink(self, data):
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setattr(data, '_sa_adapter', None)
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def adapt_like_to_iterable(self, obj):
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def append_with_event(self, item, initiator=None):
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self.collection.add(item, emit=initiator)
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def append_multiple_without_event(self, items):
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self.collection.members.extend(items)
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def append_without_event(self, item):
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self.collection.add(item, emit=False)
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def remove_with_event(self, item, initiator=None):
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self.collection.remove(item, emit=initiator)
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def remove_without_event(self, item):
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self.collection.remove(item, emit=False)
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def clear_with_event(self, initiator=None):
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for item in list(self):
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self.remove_with_event(item, initiator)
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def clear_without_event(self):
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for item in list(self):
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self.remove_without_event(item)
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return iter(self.collection)
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def fire_append_event(self, item, initiator=None):
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if initiator is not False and item is not None:
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self.state.get_impl(self.key).\
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fire_append_event(self.state, self.state.dict, item,
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def fire_remove_event(self, item, initiator=None):
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if initiator is not False and item is not None:
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self.state.get_impl(self.key).\
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fire_remove_event(self.state, self.state.dict, item,
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def fire_pre_remove_event(self, initiator=None):
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self.state.get_impl(self.key).\
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fire_pre_remove_event(self.state, self.state.dict,
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class MyCollection(object):
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self.members = list()
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def add(self, object, emit=None):
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self.members.append(object)
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collection_adapter(self).fire_append_event(object, emit)
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def remove(self, object, emit=None):
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collection_adapter(self).fire_pre_remove_event(object)
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self.members.remove(object)
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collection_adapter(self).fire_remove_event(object, emit)
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def __getitem__(self, index):
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return self.members[index]
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return iter(self.members)
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return len(self.members)
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if __name__ == '__main__':
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meta = MetaData(create_engine('sqlite://'))
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engine = create_engine('sqlite://')
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table1 = Table('table1', meta,
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Column('id', Integer, primary_key=True),
added
removed
examples/custom_attributes/custom_management.py
