@classmethod
def get_elasticsearch_schema(clz, _es_version):
    """
        Returns the elasticsearch schema for the _invenio_explicit_acls property.

        The property looks like::

            _invenio_explicit_acls [{
               "timestamp": "...when the ACL has been applied to the resource",
               "acl": <id of the acl>,
               "operation": name of the operation
                user: [1, 2, 3]
            }]

        :return:
        """
    return {'type': 'integer'}
