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 _drop_schema(self, force_drop=False):
        """ Drops the schema"""
        connection = connections[get_tenant_database_alias()]
        has_schema = hasattr(connection, 'schema_name')
        if has_schema and connection.schema_name not in (self.schema_name, get_public_schema_name()):
            raise Exception("Can't delete tenant outside it's own schema or "
                            "the public schema. Current schema is %s."
                            % connection.schema_name)

        if has_schema and schema_exists(self.schema_name) and (self.auto_drop_schema or force_drop):
            self.pre_drop()
            cursor = connection.cursor()
            cursor.execute('DROP SCHEMA "%s" CASCADE' % self.schema_name)