def METHOD_NAME(self) -> dict[str, Any]:
    """
    Register classes that inherits from DatastoreBackend.
    Every registered class provides implementations of DatastoreBackend
    and, depending on `datastore.write_url`, one of them will be used
    inside actions.
    `ckanext.datastore.DatastoreBackend` has method `set_active_backend`
    which will define most suitable backend depending on schema of
    `ckan.datastore.write_url` config directive. eg. 'postgresql://a:b@x'
    will use 'postgresql' backend, but 'mongodb://a:b@c' will try to use
    'mongodb' backend(if such backend has been registered, of course).
    If read and write urls use different engines, `set_active_backend`
    will raise assertion error.
    :returns: the dictonary with backend name as key and backend class as
              value
    """
    return {}