Django：怎么样 <classname> 在models.Model子类中创建的_set属性？

Question

In Django, I can have a model Question and a model Choice:

class Question(models.Model):
    ...
    def __str__(self):
        return self.question_text

class Choice(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    ...
    def __str__(self):
        return choice_text

I can then do this:

>>>q = Question(question_text = 'How are you?', pub_date = timezone.now())
>>>q.choice_set.all()
<QuerySet []>

The q.choice_set , according to my understanding, accesses the set of Choice objects in our database which refer to q by their foreign key.

My question is: How is the choice_set attribute being created? I've never seen a attribute name taking the name of another class in lower case letters. How is this achieved?

EDIT: To clarify, I'm asking about how Django sets the name of the variable dynamically, not the variable contents.

Answer 1

The name is decided by ForeignObjectRel.get_accessor_name . The actual attribute is set via setattr() in RelatedField.contribute_to_related_class .

Essentially, this happens when you create an instance of ForeignKey :

attribute_name = YourModel._meta.model_name + '_set'
setattr(foreign_key, attribute_name, SomeDescriptorClass(foreign_key))