manytomany 的 Django 聚合总和正在将其字段中的所有内容相加，而不是选择的内容

Question

2 类涉及问题 class 约会和 class 服务

appointmentApp.models class 服务

class Service(models.Model):
    service_name = models.CharField(max_length=15, blank=False)
    service_time = models.IntegerField(blank=False)
    
    def __str__(self):
        return self.service_name

    class Meta:
        verbose_name_plural = "Services"

appointmentApp/models.py class 约会

class Appointment(models.Model):
    service_chosen = models.ManyToManyField(Service, blank=False)
    total_time = models.IntegerField(blank=False, null=False, default=0)

    #will add up the amount of time needed for each service
    def save(self, *args, **kwargs):
        self.total_time += Service.objects.all().aggregate(total_time=Sum('service_time'))['total_time']
        super(Appointment, self).save(*args, **kwargs)

    def __str__(self):
        return self.client_dog_name

通过多项选择字段选择服务，并在保存时添加 service_chosen 的 service_time

但是我的保存功能所做的是将所有现有的 service.service_time 而不是所选的相加，为什么会这样？

Answer 1

ManyToManyFields 被保存在保存包含实例之后，您需要创建一个信号处理程序来在 m2m_changed

上执行此更新

from django.db.models.signals import m2m_changed


class Appointment(models.Model):
    ...


def service_chosen_changed(sender, instance=None, action=None, **kwargs):
    if action == 'post_add':
        instance.total_time = instance.service_chosen.aggregate(total_time=Sum('service_time'))['total_time']
        instance.save()

m2m_changed.connect(service_chosen_changed, sender=Appointment.service_chosen.through)

manytomany 的 Django 聚合总和正在将其字段中的所有内容相加，而不是选择的内容

Django aggregate sum of manytomany is adding up everything in its field instead of the ones selected

django

django-models