docs: def all_entity_classes():
      """Return the list of all concrete persistent classes that are subclasses
      of Entity."""
      persistent_classes = Entity._decl_class_registry.values()
      # with sqlalchemy 0.8 _decl_class_registry holds object that are not
      # classes
      return [
          cls for cls in persistent_classes if isclass(cls) and issubclass(cls, Entity)
      ]