""" Illustrates an extension which creates version tables for entities and stores records for each change. The same idea as Elixir's versioned extension, but more efficient (uses attribute API to get history) and handles class inheritance. The given extensions generate an anonymous "history" class which represents historical versions of the target object. Usage is illustrated via a unit test module ``test_versioning.py``, which can be run via nose:: cd examples/versioning nosetests -v A fragment of example usage, using declarative:: from history_meta import Versioned, versioned_session Base = declarative_base() class SomeClass(Versioned, Base): __tablename__ = 'sometable' id = Column(Integer, primary_key=True) name = Column(String(50)) def __eq__(self, other): assert type(other) is SomeClass and other.id == self.id Session = sessionmaker(bind=engine) versioned_session(Session) sess = Session() sc = SomeClass(name='sc1') sess.add(sc) sess.commit() sc.name = 'sc1modified' sess.commit() assert sc.version == 2 SomeClassHistory = SomeClass.__history_mapper__.class_ assert sess.query(SomeClassHistory).\\ filter(SomeClassHistory.version == 1).\\ all() \\ == [SomeClassHistory(version=1, name='sc1')] The ``Versioned`` mixin is designed to work with declarative. To use the extension with classical mappers, the ``_history_mapper`` function can be applied:: from history_meta import _history_mapper m = mapper(SomeClass, sometable) _history_mapper(m) SomeHistoryClass = SomeClass.__history_mapper__.class_ """