Django 模型与Python 类属性

2022-01-13 00:00:00 python django attributes

问题描述

django 网站上的教程显示了模型的以下代码:

The tutorial on the django website shows this code for the models:

from django.db import models

class Poll(models.Model):
    question = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice = models.CharField(max_length=200)
    votes = models.IntegerField()

现在,这些属性中的每一个都是类属性,对吧?因此,该类的所有实例都应共享相同的属性.稍后,他们展示了这段代码:

Now, each of those attribute, is a class attribute, right? So, the same attribute should be shared by all instances of the class. A bit later, they present this code:

class Poll(models.Model):
    # ...
    def __unicode__(self):
        return self.question

class Choice(models.Model):
    # ...
    def __unicode__(self):
        return self.choice

它们是如何从类属性转变为实例属性的?我是不是把类属性弄错了?

How did they turn from class attributes into instance attributes? Did I get class attributes wrong?


解决方案

看看django/db/models.py下的Model类.在那里,类属性通过类似的方式转换为实例属性

Have a look at the Model class under django/db/models.py. There the class attributes are turned to instance attributes via something like

setattr(self, field.attname, val)

人们可能会推荐整个文件(ModelBaseModel 类)作为元类的优秀实践示例.

One might recommend the whole file (ModelBase and Model class) as an excellent hands-on example on metaclasses.

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