Django多到多序

Question

我有两个表主题表和日表。主题列表是白天的m2m。所以我的问题是我正在制定学校时间表。因此，对于每一天不同的主题，当我在每一天添加主题时，主题的顺序是相同的。

#Models.py

class SubjectList(models.Model):
    subject_name = models.CharField(max_length=25)

    def __str__(self):
        return self.subject_name

class Day(models.Model):
    day_name = models.CharField(max_length=15)
    subject_name = models.ManyToManyField(SubjectList)
    class_number = models.ForeignKey(AddClass, on_delete=models.CASCADE, null=True, blank=True)
    start_time = models.TimeField(null=True, blank=True)
    end_time = models.TimeField(null=True, blank=True)

    def __str__(self):
        return self.class_number.class_number

#Views.py

class TimeTableView(APIView):
    def get(self, request, id):
        class_number = AddClass.objects.get(id=id)
        day = Day.objects.filter(class_number=class_number.id)
        print(day)
        serializer = DaySerializer(day, many=True)
        return Response(serializer.data)

我想这样做

星期一-英语，数学，科学，社会科学星期二-数学，社会科学，英语，数学

但我就是这样

星期一-英语，数学，科学，社会科学星期二-英语，数学，科学，社会科学

​

​

即使按不同的顺序添加主题，两者的顺序也是相同的。

Answer 1

可以向M2M表中添加更多字段，方法是声明模型并将其分配给具有直通参数的M2M关系。

class DaySubjectList(models.Model):
    day =  models.ForeignKey(Day, on_delete=models.CASCADE, related_name="day_subject_lists")
    subject_list =  models.ForeignKey(SubjectList, on_delete=models.CASCADE, related_name="day_subject_lists")
    order = models.IntegerField(default=0)

class Day(models.Model):
    day_name = models.CharField(max_length=15)
    subject_name = models.ManyToManyField(SubjectList, through=DaySubjectList)
    class_number = models.ForeignKey(AddClass, on_delete=models.CASCADE, null=True, blank=True)
    start_time = models.TimeField(null=True, blank=True)
    end_time = models.TimeField(null=True, blank=True)

    def __str__(self):
        return self.class_number.class_number    

可以使用相关管理器的through_defaults参数设置order字段。

my_day.subject_name.add(my_subject, through_defaults={"position": my_position})

您可以使用related_name订购

Day.objects.filter(class_number=class_number.id).prefetch_related(Prefetch("day_subject_lists", queryset=DaySubjectList.objects.order_by("position")))

只有当您访问my_day.day_subject_lists.all()而不是my_day.subject_name.all()时，才会排序记录

如果更方便的话，您可以将这些记录以另一个名称存储。

Day.objects.filter(class_number=class_number.id).prefetch_related(Prefetch("day_subject_lists", queryset=DaySubjectList.objects.order_by("position"), to_attr="my_prefered_name"))

请注意，my_day.my_prefered_name是一个列表，而不是查询，所以不要使用.all()来访问它。

使用您的模型相互引用有任何问题，您可以使用字符串synthax。

class DaySubjectList(models.Model):
    day =  models.ForeignKey("myapp.Day", on_delete=models.CASCADE, related_name="day_subject_lists")
    subject_list =  models.ForeignKey("myapp.SubjectList", on_delete=models.CASCADE, related_name="day_subject_lists")
    order = models.IntegerField(default=0)

Answer 2

You need to specify an order for the m2m relation [Django-doc]:
class Day(models.Model):
    # ...
    subject_name = models.ManyToManyField(
        SubjectList,
        ordered=True
    )
    # ...
Now if you query a Day object, the related SubjectList objects will be ordered in the order you added these.
You can further alter the order with .move(...), or .reorder(...).
Note: You should rename the subject_name field to subjects, since it relates to multiple SubjectList objects. A ForeignKey or OneToOneField indeed often uses the _name suffix, since these relate to at most one other object, but a ManyToManyField does not have this limitation.

Note: You should not use ForeignKey(.., null=True)s. A foreign key represents a relation, and a relation can not be "NULL". You should make these fields not nullable, and make the related model have a nullable parent relation (with null=True), or make the field optional with blank=True.