@contextlib.contextmanager
def sqlite_disable_foreign_keys(engine):
    """Temprorary disable foreign keys

    This context manager allows one to temprorary disable checking of
    foreign keys in SQLite. This is actually very useful, because we
    recreate the original table in order to drop constraints or columns,
    which leads to breaking of existing foreign keys.

    """

    engine.execute('PRAGMA foreign_keys = OFF;')
    yield
    engine.execute('PRAGMA foreign_keys = ON;')