以互惠的方式连接两个模型

Question

I'm trying to create a LMS (learning management system) system for my school. In this system I'm trying to connect between origen_classroom model and the students and teacher model in a way that updating one of the models will update the others. I try to use signals but it doesnt work on this model (It's working on the user model) attached is my code:

from django.db import models
from django.contrib.auth.models import AbstractUser
from django.dispatch import receiver
from django.db.models.signals import post_save
from .utils import upload_location, phone_regex
from materials.models import Subject


# Add fields to user module and uplaod image to the media location
class User(AbstractUser):
    USER_TYPE_CHOICES = (
        (1, 'student'),
        (2, 'teacher'),
    )
    user_type = models.PositiveSmallIntegerField(choices=USER_TYPE_CHOICES,
                                                 blank=True,
                                                 null=True
                                                 )  # user type
    date_of_birth = models.DateField(blank=True, null=True)
    phone_number = models.CharField(validators=[phone_regex],
                                    max_length=11,
                                    blank=True
                                    )  # validators should be a list
    profile_image = models.ImageField(upload_to=upload_location,
                                      blank=True,
                                      default='test.png',
                                      height_field='height_field',
                                      width_field='width_field',
                                      )
    height_field = models.IntegerField(default=0)
    width_field = models.IntegerField(default=0)

    class Meta:
        verbose_name_plural = "Users"

    def __str__(self):
        return self.username

# main student module


class Student(models.Model):
    user = models.OneToOneField(
        User, related_name='student', on_delete=models.CASCADE)
    origen_class = models.ForeignKey(
        'OrigenClass', on_delete=models.SET_NULL, blank=True, null=True)

    def __str__(self):
        return self.user.username

# main teacher module


class Teacher(models.Model):
    user = models.OneToOneField(
        User, related_name='teacher', on_delete=models.CASCADE)
    head_class = models.OneToOneField('OrigenClass', on_delete=models.SET_NULL, blank=True, null=True)
    teacher_subject = models.ForeignKey(Subject, on_delete=models.CASCADE, blank=True, null=True)

    def __str__(self):
        return self.user.username

# using signal to save changes in users into students or teachers
# TBD when changing from teacher to student need to check if already exist in one list and delete him
@receiver(post_save, sender=User)
def append_to_user_type(sender, **kwargs):
    if kwargs.get('created', False):
        if kwargs.get('instance').user_type == 2:
            Teacher.objects.get_or_create(user=kwargs.get('instance'))
        elif kwargs.get('instance').user_type == 1:
            Student.objects.get_or_create(user=kwargs.get('instance'))
    elif not kwargs.get('instance')._state.adding:
        if kwargs.get('instance').user_type == 2:
            Teacher.objects.get_or_create(user=kwargs.get('instance'))
        elif kwargs.get('instance').user_type == 1:
            Student.objects.get_or_create(user=kwargs.get('instance'))


class Grade(models.Model):
    GRADE_CHOICES = (
        (1, 'Grade 10'),
        (2, 'Grade 11'),
        (3, 'Grade 12'),
    )
    grade = models.PositiveSmallIntegerField(
        choices=GRADE_CHOICES, blank=True, null=True)  # Grade type

    def __str__(self):
        return self.GRADE_CHOICES[self.grade - 1][1]


class OrigenClass(models.Model):
    grade = models.ForeignKey(
        Grade, related_name='Grade', on_delete=models.CASCADE)
    class_name = models.PositiveIntegerField(blank=True, null=True)
    head_teacher = models.OneToOneField(
        Teacher, related_name='head_teacher', on_delete=models.CASCADE)
    students_members = models.ManyToManyField(Student, related_name='students')

    def __str__(self):
        return f'{self.grade} Class {self.class_name}'

@receiver(post_save, sender=Teacher)
def append_head_teacer_toclass(sender, **kwargs):
    if kwargs.get('created', False):
        OrigenClass.objects.get_or_create(head_teacher=kwargs.get('instance'))
    elif not kwargs.get('instance')._state.adding:
        OrigenClass.objects.get_or_create(head_teacher=kwargs.get('instance'))

Answer 1

I think you have some errors in your append_head_teacer_toclass(sender, **kwargs) . When you are trying to create the OriginClass instance you are missing some mandatory fields which cannot be None , eg grade.

So when you are saving a Teacher instance where the OriginClass has not been set this should raise an error.

If the associated OriginClass instance already exists, you are just getting the instance, not updating anything. To update an instance you should use update_or_create .