Django模型和放大器; Python类属性 [英] Django models & Python class attributes

问题描述

Django的网站上的教程演示了这个code代表机型：

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，每一个这些属性，是一个类属性，对不对？所以，相同的属性应该由类的所有实例共享。过了一会儿，他们present这个code：

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

他们怎么会从阶级属性转成实例属性？我才拿到类属性错了？

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

推荐答案

有一个看模式下的Django / DB / models.py 类。通过一些有阶级属性转向实例属性如

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)

有人可能会建议将整个文件（模型库和模式类）作为一个优秀的动手例如在元类

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

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