mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-28 11:35:19 -04:00
Mike Bayer
112 lines
3.0 KiB
Python
112 lines
3.0 KiB
Python
"""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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"""
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from sqlalchemy import create_engine, MetaData, Table, Column, Integer, Text,\
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ForeignKey
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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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del_attribute
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from sqlalchemy.orm.instrumentation import is_instrumented
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from sqlalchemy.ext.instrumentation import InstrumentationManager
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class MyClassState(InstrumentationManager):
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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 install_state(self, class_, 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 instance.__dict__['_goofy_dict']['state']
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return find
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class MyClass(object):
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__sa_instrumentation_manager__ = MyClassState
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def __init__(self, **kwargs):
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for k in kwargs:
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setattr(self, k, kwargs[k])
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def __getattr__(self, key):
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if is_instrumented(self, key):
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return get_attribute(self, key)
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else:
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try:
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return self._goofy_dict[key]
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except KeyError:
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raise AttributeError(key)
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def __setattr__(self, key, value):
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if is_instrumented(self, key):
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set_attribute(self, key, value)
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else:
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self._goofy_dict[key] = value
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def __delattr__(self, key):
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if is_instrumented(self, key):
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del_attribute(self, key)
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else:
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del self._goofy_dict[key]
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if __name__ == '__main__':
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engine = create_engine('sqlite://')
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meta = MetaData()
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table1 = Table('table1', meta,
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Column('id', Integer, primary_key=True),
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Column('name', Text))
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table2 = Table('table2', meta,
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Column('id', Integer, primary_key=True),
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Column('name', Text),
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Column('t1id', Integer, ForeignKey('table1.id')))
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meta.create_all(engine)
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class A(MyClass):
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pass
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class B(MyClass):
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pass
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mapper(A, table1, properties={
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'bs': relationship(B)
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})
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mapper(B, table2)
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a1 = A(name='a1', bs=[B(name='b1'), B(name='b2')])
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assert a1.name == 'a1'
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assert a1.bs[0].name == 'b1'
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sess = Session(engine)
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sess.add(a1)
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sess.commit()
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a1 = sess.query(A).get(a1.id)
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assert a1.name == 'a1'
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assert a1.bs[0].name == 'b1'
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a1.bs.remove(a1.bs[0])
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sess.commit()
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a1 = sess.query(A).get(a1.id)
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assert len(a1.bs) == 1
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