Question

我想知道如何计算与某个ClassRoom相关的学生人数，并将当前数量放在一个字段中，这样每当我将学生添加到ClassRoom时，我都可以知道当前的学生人数在它。

  class Student(models.Model):
        ClassRoom = models.ForeignKey(ClassRoom)


    class ClassRoom(models.Mode):
       qtt_current_students =

------------编辑------------------

我尝试了以下内容，但qtt_current_students没有得到 instance.ClassRoom.student_set.count（）

每当我添加学生时，该字段都没有

@receiver(pre_save, sender=Student)
def Student_pre_save(sender, instance, **kwargs):
    instance.ClassRoom.qtt_current_students = instance.ClassRoom.student_set.count()

Answer 1

@receiver(post_save, sender=Student)
def Student_pre_save(sender, instance, **kwargs):
    ClassRoom.qtt_current_students = instance.ClassRoom.student_set.count()

试试这个，

Answer 2

我试过这个，效果很好。

@receiver(post_save, sender=Student)
def student_post_save(sender, instance, **kwargs):
    t = ClassRoom.objects.get(pk=instance.ClassRoom.pk)
    t.qtt_current_students = instance.ClassRoom.student_set.count()
    t.save()

@receiver(post_delete, sender=Student)
def student_post_delete(sender, instance, **kwargs):
    t = ClassRoom.objects.get(pk=instance.ClassRoom.pk)
    t.qtt_current_students = instance.ClassRoom.student_set.count()
    t.save()

如何计算并将与表相关的对象返回到模型字段

2 个答案: