def on_header(self, metadata):
        self._keys = metadata["fields"]
Return all photos that belong to this gallery but don't share the
dataset/ETHPy150Open nigelsmall/py2neo/py2neo/database/__init__.py/BoltDataSource.on_header--crossover with--dataset/ETHPy150Open jdriscoll/django-photologue/photologue/models.py/Gallery.orphaned_photos