March 2022
Intermediate to advanced
522 pages
13h 52m
Chinese
Content preview from Python语言及其应用（第2版）
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280
｜
第
16
章
• SQLAlchemy
表达式语言
• SQLAlchemy ORM
使用
ORM
来
避免
SQL
的复杂性，似乎是一个自然而然的选择。你该这么做吗？有人认
为应该避免使用
ORM
，但也有人觉得这种批评过头了
。不管谁对谁错，
ORM
都是一种
抽象概念，而所有的抽象概念都是有漏洞的，在某些时候会出问题。当
ORM
不能满足你
的需求时，必须弄清楚其工作原理以及如何在
SQL
中修复
。可以借用如下这则网络迷因
（
Internet meme
）
3
。
有些人在碰到问题时会想：“我知道我得使用
ORM
。
”那么，他们现在有两个问
题了。
将
ORM
用于简单应用或是能将数据直接映射到数据库表的应用
。如果应用足够简单，你
也许可以考虑使用直截了当的
SQL
或
SQL
表达式语言。
16.5.7
其他数据库访问包
如果你在寻找能处理多个数据库的
Python
工具，希望功能比
db-api
多，但又不要像
SQLAlchemy
那么繁杂，以下两个包值得考虑。
•
dataset
宣称其目标是“懒人的数据库”。它在
SQLAlchemy
的基础上提供了可用于
SQL
、
JSON
和
CSV
存储的简单
ORM
。
•
records
宣称其目标是“凡人的
SQL
”。它只提供了
SQL
查询，在内部使用
SQLAlchemy
处理
SQL
方言问题
、连接池以及其他细节。
records
集成了
tablib
（参见
16.3.7
节），允
许你将数据导出为
CSV
、
JSON
和其他格式。
16.6 NoSQL
数据存储
关系数据库是矩形的，但是数据的形式各异，如果不做大量的努力和调整，可能很难适
应。这是一个方钉 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.