《Django 5 By Example》学习第 11 天，p237-p338 总结，总计 102 页。

一、技术总结

1.follow system(关注功能)

表之间的关系有三种：OneToOneField，many-to-one(使用 Foreignkey())，ManyToManyField。有时候为了更好的描述对象之间的关系，需要多创建一张中间表：Creating an intermediate model is necessary when you want to store additional information on the relationship, for example, the date when the relationship was created, or a field that describes the nature of the relationship。

例如关注功能：

class Contact(models.Model):
    user_from = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='rel_from_set')
    user_to = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='rel_to_set')
    created = models.DateTimeField(auto_now_add=True)


    class Meta:
        indexes = [
            models.Index(fields=['-created']),
         ]
        ordering = ['-created']


    def __str__(self):
        return f'{self.user_from.username} follows {self.user_to.name}'

2.monkey patch

p289, You use the add_to_class() method of Django models to monkey patch the User model。monkey patch 的意思是：Monkey patch is a technique used to dynamically update the code at runtime without altering the source code。示例：

# monkey patch 示例
user_model = get_user_model()
user_model.add_to_class(
    'following',
    models.ManyToManyField('self', through=Contact, symmetrical=False, related_name='followers')
)

注：尽量少用 monkey patch。

3.activity stream(活动流)功能

4.contenttypes

p300, contenttypes 的作用：This application can track all models installed in your project and provides a generic interface to interact with your models.

5.denormalization(反规范化)

p315, Denormalization is making data redundant in such a way that it optimizes read performance. For example, you might be copying related data to an object to avoid expensive read queries to the database when retrieving the related data.

6.signal

7.django-debug-toolbar

用于完善 debug 功能，在界面通过 toolbar 显示一些统计信息。个人觉得在实际开发中可有可无。

8.使用 redi 做缓存

使用的 package 名称也叫 redis。在实际业务也中经常使用，但是不复杂，掌握常用的方法即可。

二、英语总结(生词：2)

1.thewart

p292. Usernames, unlike sequential IDs, thwart enumeration attacks by obscuring your data structure.

vt. to stop sth from happing.

2.every once in a while

p327, Redis stores everything in memory, but the data can be persisted by dumping the dataset to disk every once in a while, or by adding each command to a log.

idiom. sometimes, but not regularly. 也写作 every so often。

三、其它

chapter 07 简评：4-7 章是一个完整的项目(bookmarks)，建议从第 4 章按顺序阅读到第 7 章，不要跳过某个章节，因为作者的代码是连续，跳过之后项目可能无法运行。

Pycharm(2024.3 Professional Edition) ：Settings > Build, Execution, Deployment > Python Debugger 新增了一个功能 "Run debugger in server mode"，然后 Pycharm 默认是勾选的，导致我在 WSL 使用 debug 启动后一直无法访问。忍了那么久终于可以 debug 了，气 die! Pycharm，你再这样我明年就不续费了。

四、参考资料

1. 编程

(1) Antonio Melé，《Django 5 By Example》：https://book.douban.com/subject/37007362/

2. 英语

(1) Etymology Dictionary：https://www.etymonline.com

(2) Cambridge Dictionary：https://dictionary.cambridge.org

欢迎搜索及关注：编程人(a_codists)