django related field subset average

Question

i have two models in django app

UserDay model:

class UserDay(models.Model):
   date = DateField()

   @property
   def avg(self):
      return self.activities.aggregate(Avg('point'))

Activity model:

class Activity(models.Model):
   point = models.SmallIntegerField()

   userDay = models.ForeignKey(
      UserDay, on_delete=models.CASCADE, related_name="activities"
   )

a user day can have "n" activities. i just want to get average of last "m" activities point.

HOW CAN I DO IT?? :D

Answer 1

Since you need a average of last m activities, we can get the all activities in realtion with UserDay and sort in decreasing order for m objects.

class UserDay(models.Model):


date = DateField()

   @property
   def avg(self):
      return self.activities.order_by('-id')[:m].aggregate(Avg('point'))