how to add correspondence between two models
for example, the following two classes:

from django.db import models

class Question(models.Model):
    class Meta:
        verbose_name = ""
        verbose_name_plural = ""
    question_text = models.CharField("",max_length = 100)
    pub_date = models.DateTimeField("")
    def __str__(self):
        return self.question_text

class Choice(models.Model):
    class Meta:
        verbose_name = ""
        verbose_name_plural = ""
    def __str__(self):
        return self.choice_text
    question = models.ForeignKey(Question, on_delete = models.CASCADE)
    choice_text = models.CharField("",max_length = 50)
    votes = models.IntegerField("",default = 0)

one-to-one relationship to Question is defined in Choice .
according to the train of thought, one-to-many relationship to Choice should be added to Question
, but if it is added in Question , because the Choice class has not been defined yet, it will report an error
.