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 db_version_control(engine, abs_path, version=None):
    """Mark a database as under this repository's version control.

    Once a database is under version control, schema changes should
    only be done via change scripts in this repository.

    :param engine:  SQLAlchemy engine instance for a given database
    :param abs_path: Absolute path to migrate repository
    :param version:  Initial database version
    """
    repository = _find_migrate_repo(abs_path)
    versioning_api.version_control(engine, repository, version)
    return version