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?
推荐答案
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(ModelBase 和 Model 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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