'Return a :class:`.Query` that will expire and refresh all instances
as they are loaded, or reused from the current :class:`.Session`.
:meth:`.populate_existing` does not improve behavior when
the ORM is used normally - the :class:`.Session` object\'s usual
behavior of maintaining a transaction and expiring all attributes
after rollback or commit handles object state automatically.
This method is not intended for general use.'

@_generative()
def populate_existing(self):

    self._populate_existing = True
