[rset] New method: ResultSet.one()
This method will return exactly one entity while enforcing its existence and unicity.
The idea is shamelessly borowed from SQLAlchemy Query.one().
Closes #3352314
[jcr: use len(self) instead of len(self.rows)]
# -*- coding: utf-8 -*-# copyright %(year)s %(author)s, all rights reserved.# contact %(author-web-site)s -- mailto:%(author-email)s#%(long-license)s"""%(distname)s precreate script, executed at instance creation time or whenthe cube is added to an existing instance, before the schema is serialized.This is typically to create groups referenced by the cube'schema."""