Django:对象和model_set [英] Django: objects and model_set

问题描述

我正在学习Django 1.10官方教程第2部分

I am learning django 1.10 official tutorial part 2

class  Question(models.Model):
  # ......

class Choice(models.Model):
  question = models.ForeignKey(Question, on_delete=models.CASCADE)
  #.......

最近我看到了以下命令:-

Recent i saw the following command:-

q = Question.objects.get(id=1)
q.choice_set.all()

我的问题:-

Question实例如何包含 choice_set ，我知道它用于访问相关对象.

How Question instance contain choice_set, i know it for accessing related objects.

这为什么无效

c = Choice.objects.get(id=1)
c.question_set.all()

推荐答案

Question模型没有对Choice模型的显式引用；但是，Django自动添加反向引用，默认情况下称为choice_set.您可以通过模型上的 related_name 关键字来覆盖它，例如:

The Question model does not have an explicit reference to the Choice model; however, Django automatically adds a reverse-reference, which is by default called choice_set. You can override this by related_name keyword on the model such as:

class Choice(models.Model):
  question = models.ForeignKey(Question, on_delete=models.CASCADE, related_name='choices')

现在，您可以参考所有选择来解决这样的问题:

Now you can reference all of the choices for a question like this:

q = Question.objects.get(pk=1)
q.choices.all()

要回答第二个问题，之所以不能使用 choice 对象中的引用 question_set.all()的原因是，对于每个选择，只有一个问题加对该问题对象有一个显式引用.换句话说，选择"模型已经有一个名为"问题"的字段，该字段指向问题"模型.

To answer your second question, the reason you cannot use reference question_set.all() from a choice object is because for each choice, there is only one question plus there is an explicit reference to the question object. In other words the Choice model already has a field called Question, which points to the Question model.

希望有帮助.

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