创建另一个模型的实例时自动填充Django模型字段

Question

我有三种模型Student，Question和StudentAndQuestion

class Student(models.Model):
    class Meta:
        verbose_name_plural = "Students"
    name = models.CharField(max_length=150)
    surname = models.CharField(max_length=150)
    code = models.CharField(max_length=10)
#    group = models.ForeignKey(Group,on_delete=models.CASCADE)
    points = models.IntegerField(default=0)

class Question(models.Model):
    class Meta:
        verbose_name_plural = "Questions"

    text = models.CharField(max_length=1500)
    variants = models.CharField(max_length=1500)
    theme = models.OneToOneField(Theme, on_delete=models.CASCADE)
    anwser = models.CharField(max_length=1500)

class StudentAndQuestion(models.Model):
    question = models.OneToOneField(Question,on_delete=models.CASCADE)
    student = models.OneToOneField(Student,on_delete=models.CASCADE)
    is_learned = models.BooleanField(default=0)
    points = models.IntegerField(default=0)

当我创建学生的新实例时（例如，为所有Question创建行并将点设置为零），当我创建Question的新实例时，我希望Django将其填充到StudentAndQuestion中

Answer 1

您可以收听保存这些模型时发出的Post Save Signal ，并在处理程序中进行所需的创建。 该信号使用名为created的参数调用处理程序，如果创建了新记录，则该参数为True 。

请参阅有关信号的文档以了解如何注册您的处理程序。 样本如下

from django.db.models.signals import post_delete, post_save

from .models import Student, Question, StudentAndQuestion


def add_question_to_students(sender, instance, created, *args, **kwargs):    
question = instance
if created:
    StudentAndQuestion.objects.bulk_create([
        StudentAndQuestion(question=question, student_id=student_id)
        for student_id in Student.objects.values_list("id", flat=True)
    ])

def add_student_to_question(sender, instance, created, *args, **kwargs):    
student = instance
if created:
    StudentAndQuestion.objects.bulk_create([
        StudentAndQuestion(question=question_id, student=student)
        for question_id in Question.objects.values_list("id", flat=True)
    ])

post_save.connect(add_question_to_students, sender=Question)
post_save.connect(add_student_to_question, sender=Student)

或者，您可以覆盖两个模型中的保存以执行相同的操作

class Question(models.Model):
    ....
    def save(*args, **kwargs):
        is_create = self.pk is None
        instance = super().save(*args, **kwargs)
        add_question_to_students(Question, self, is_created)

class Student(models.Model):
    ....
    def save(*args, **kwargs):
        is_create = self.pk is None
        instance = super().save(*args, **kwargs)
        add_student_to_question(Student, self, is_created)

我觉得后面的内容比较清晰，因为更容易找出保存时的所有情况，但是如果模型位于不同的应用程序中，则会导致循环依赖。