'Returns sum of reviewer points since the given datetime.'

@classmethod
def get_performance_since(cls, user, since):

    key = cls.get_key(('get_performance:%s:%s' % (user.id, since.isoformat())))
    val = cache.get(key)
    if (val is not None):
        return val
    sql = '\n                                                    SELECT    `reviewer_scores`.*,\n                                                                                SUM(`reviewer_scores`.`score`)    AS    `total`\n                                                    FROM    `reviewer_scores`\n                                                    LEFT    JOIN    `addons`    ON    (`reviewer_scores`.`addon_id`=`addons`.`id`)\n                                                    WHERE    `reviewer_scores`.`user_id`    =    %s    AND\n                                                                            `reviewer_scores`.`created`    >=    %s\n                                                    ORDER    BY    `total`    DESC\n                                '
    val = list(ReviewerScore.objects.raw(sql, [user.id, since]))
    cache.set(key, val, 3600)
    return val
