def insertDomain(self, domain, indegree=0, outdegree=0):
		'''增加一个域名'''
		cur = self.conn.cursor()
		cur.execute("INSERT INTO Domains VALUES (NULL,?,?,?)", (domain, indegree, outdegree))
		# 写入到文件中
		self.conn.commit()
def __exit__(self, exc_type, exc_val, exc_tb):
        connection = connections[get_tenant_database_alias()]

        connection.set_tenant(self._previous_tenant.pop())