如何在django post\u save上使用update\u或\u create？

插入数据工作正常，但当我更新现有数据时，它会创建另一条记录，而不是更新

我尝试的是@ruddra先生的解决方案

class StudentsEnrolledSubject(models.Model):
        Students_Enrollment_Records = models.ForeignKey(StudentsEnrollmentRecord, related_name='+',
                                                        on_delete=models.CASCADE, null=True)
        Subject_Section_Teacher = models.ForeignKey(SubjectSectionTeacher, related_name='+', on_delete=models.CASCADE,
                                                    null=True,blank=True)      

    @receiver(post_save, sender=StudentsEnrollmentRecord)
            def create(sender, instance, created, *args, **kwargs):
                teachers = SubjectSectionTeacher.objects.filter(Sections=instance.Section,
                                                                Education_Levels=instance.Education_Levels,
                                                                Courses=instance.Courses)
            for each in teachers:
                if created or teachers.exists():
                    print("if")
                    StudentsEnrolledSubject.objects.create_or_update(
                        pk=each.id,
                        Students_Enrollment_Records=instance,
                        Subject_Section_Teacher=each

                    )

它起作用了！但当我试图保存另一条包含多个相关数据的记录时，它只保存了一条记录。

在您的代码中：

            StudentsEnrolledSubject.objects.update_or_create(
                Students_Enrollment_Records=instance,
                defaults= {'Subject_Section_Teacher': each}

            )

---

更新： 我认为你不应该使用

update\u或\u create

信号。如果您使用

update\u或\u create

，当您更改

StudentsEnrollmentRecord

的课程或教育水平等时，教师人数也将不相同

要获取旧实例，请使用

pre_save

信号：

StudentsEnrolledSubject.objects.update_or_create(
    Students_Enrollment_Records=instance,
    defaults= {'Subject_Section_Teacher':each}
)

---

在这里，我删除了所有

学生注册主题

，如果

课程

，

部分

，

教育水平

中的任何值与旧实例不同。因为正如我前面所说的，教师的数量将不一样。因此，我删除了这些实例，并与新教师创建了新实例。

应该是

update\u或\u create

：）请查看更新的答案，先生，但是当我保存时，我的数据库中只保存了一条记录，当我删除pk=each.id时，只保存了一条记录，请查看更新部分，最好谨慎使用。请确保在使用数据库之前对其进行备份。因为您可能会丢失数据I get此错误sir无法从此行“old_instance=StudentsEnrollmentRecord.objects.get（instance.pk）”解包不可iterable的非类型对象

StudentsEnrolledSubject.objects.update_or_create(
    Students_Enrollment_Records=instance,
    defaults= {'Subject_Section_Teacher':each}
)

class StudentsEnrollmentRecord(models.Model):
    # ...

    @receiver(pre_save, sender=StudentsEnrollmentRecord)
    def get_older_instance(sender, instance, *args, **kwargs):
        try:
           instance._old_instance = StudentsEnrollmentRecord.object.get(pk=instance.pk)
        except StudentsEnrollmentRecord.DoesNotExist:
           instance._old_instance = None

    @receiver(post_save, sender=StudentsEnrollmentRecord)
    def create(sender, instance, created, *args, **kwargs):
        if not created:
           old_instance = instance._old_instance
           if older_instance.Courses != instance.Courses or \
              older_instance.Sections != instance.Sections or \
              older_instance.Education_Levels != instance.Education_Levels:

                 StudentsEnrolledSubject.objects.filter(
                   Students_Enrollment_Records=instance
                 ).delete()
           else:
               return None


       teachers = SubjectSectionTeacher.objects.filter(Sections=instance.Section,  Education_Levels=instance.Education_Levels, Courses=instance.Courses)
       for each in teachers:
             StudentsEnrolledSubject.objects.create(
                Students_Enrollment_Records_id=instance.pk,
                Subject_Section_Teacher=each
             )