mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-13 04:07:20 -04:00
Mike Bayer
74 lines
2.1 KiB
Python
74 lines
2.1 KiB
Python
"""
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Illustrates an extension which creates version tables for entities and stores
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records for each change. The same idea as Elixir's versioned extension, but
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more efficient (uses attribute API to get history) and handles class
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inheritance. The given extensions generate an anonymous "history" class which
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represents historical versions of the target object.
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Usage is illustrated via a unit test module ``test_versioning.py``, which can
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be run via nose::
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nosetests -w examples/versioning/
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A fragment of example usage, using declarative::
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from history_meta import VersionedMeta, VersionedListener
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Base = declarative_base(metaclass=VersionedMeta, bind=engine)
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Session = sessionmaker(extension=VersionedListener())
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class SomeClass(Base):
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__tablename__ = 'sometable'
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id = Column(Integer, primary_key=True)
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name = Column(String(50))
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def __eq__(self, other):
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assert type(other) is SomeClass and other.id == self.id
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sess = Session()
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sc = SomeClass(name='sc1')
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sess.add(sc)
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sess.commit()
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sc.name = 'sc1modified'
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sess.commit()
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assert sc.version == 2
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SomeClassHistory = SomeClass.__history_mapper__.class_
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assert sess.query(SomeClassHistory).\\
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filter(SomeClassHistory.version == 1).\\
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all() \\
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== [SomeClassHistory(version=1, name='sc1')]
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To apply ``VersionedMeta`` to a subset of classes (probably more typical), the
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metaclass can be applied on a per-class basis::
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from history_meta import VersionedMeta, VersionedListener
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Base = declarative_base(bind=engine)
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class SomeClass(Base):
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__tablename__ = 'sometable'
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# ...
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class SomeVersionedClass(Base):
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__metaclass__ = VersionedMeta
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__tablename__ = 'someothertable'
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# ...
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The ``VersionedMeta`` is a declarative metaclass - to use the extension with
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plain mappers, the ``_history_mapper`` function can be applied::
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from history_meta import _history_mapper
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m = mapper(SomeClass, sometable)
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_history_mapper(m)
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SomeHistoryClass = SomeClass.__history_mapper__.class_
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""" |