First calls :meth:`find_mapping` to check if a mapping for the given
        mapped class or any of its base classes has been created. If not, a
        new one is created with a default configuration, registered
        automatically and returned.

def find_or_create_mapping(self, mapped_class):
        """
        First calls :meth:`find_mapping` to check if a mapping for the given
        mapped class or any of its base classes has been created. If not, a
        new one is created with a default configuration, registered
        automatically and returned.
        """
        mapping = self.find_mapping(mapped_class)
        if mapping is None:
            mapping = self.create_mapping(mapped_class)
            self.set_mapping(mapping)
        return mapping