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 on_backend_added(self, sender, backend_id):
        """
        Signal callback executed when a new backend is loaded

        @param sender: not used, only here to let this function be used as a
                       callback
        @param backend_id: the id of the backend to add
        """
        # Add
        backend = self.req.get_backend(backend_id)
        if not backend:
            return
        self.add_backend(backend)
        self.refresh()
        # Select
        self.select_backend(backend_id)
        # Update it's enabled state
        self.on_backend_state_changed(None, backend.get_id())