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python - 创建另一个模型的实例时自动填充 Django 模型字段

问题描述

我有三个模型 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)

我希望 Django 在我创建新的学生实例时填写 StudentAndQuestion（例如，为所有问题创建行并将点设置为零）并且当我创建新的问题实例时将其添加到所有旧学生

标签： pythondjangodatabase-design

解决方案

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。这个信号使用一个参数调用处理程序，created如果True创建了新记录，则该参数被调用。

请参阅有关信号的文档以了解如何注册您的处理程序。一个样本如下

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)

我觉得后者更清楚，因为更容易找出保存时发生的一切，但如果模型位于不同的应用程序中，它可能会导致循环依赖。

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