def robotsrulesetOfDomain(self, domain):
		'''检查domain是否在数据库中,
			否 --> (False, None)
			是 --> (True, 数据库中存储的robots.txt内容)
		'''
		exist = False
		cur = self.conn.cursor()
		# 是否存在
		cur.execute("SELECT 1 FROM Domains WHERE domain=?", (domain,))
		if cur.fetchone() :
			exist = True
		# 存在的话,结果是什么
		cur.execute("SELECT rules FROM Domains,Rulesets "
			"WHERE domain=? AND Domains.did=Rulesets.did"
			,(domain,) )
		ruleset = cur.fetchone()
		return (exist, ruleset)
def __exit__(self, exc_type, exc_value, traceback):
        connection = get_connection(self.using)
        try:
            self._no_monkey.__exit__(self, exc_type, exc_value, traceback)
        except DatabaseError:
            transaction_states[self.using].rollback()
        else:
            if not connection.closed_in_transaction and exc_type is None and \
                    not connection.needs_rollback:
                if transaction_states[self.using]:
                    transaction_states[self.using].commit()
            else:
                transaction_states[self.using].rollback()