如何在Django中按模型功能排序

Question

I have the following model:

class Player(models.Model):
    user = models.OneToOneField(User, related_name="player")
    first_name = models.CharField(max_length=128)
    last_name = models.CharField(max_length=128)

    def point_total(self):
        playerAchievements = PlayerAchievement.objects.filter(player=self)
        score = 0
        for p in playerAchievements:
            score += p.achievement.value
        return score

    def full_name(self):
        return self.first_name + ' ' + self.last_name

    def rank(self):
        print '---'
        players = Player.objects.filter(team__league=self.team.league).order_by(self.point_total())
        print self.first_name
        position = 0
        for p in players:
            position +=1

            if p.id == self.id:
                return str(position)
        return '0'

Nothing is processed past this line:

players = Player.objects.filter(team__league=self.team.league).order_by(self.point_total())

I also tried this but has the same effect:

players = self.objects.filter(team__league=self.team.league).order_by('player__point_total')

How can I order by the point total function so I can figure out the rank of each player?

Answer 1

The order_by function only operates on fields in the database, so calling a function won't work.

What you can do however is annotate the function with a Count aggregation across the ForeignKey and then order_by that:

from django.db.models import Sum

players = Player.objects.filter(team__league=self.team.league)
players = players.annotate(achievement_sum=Sum('playerachievement_set__achievement__value'))
players = players.order_by('achievement_sum')

Answer 2

You can't order querysets by methods and properties in django, you have to do the sorting by yourself in python.

players_to_sort = Player.objects.filter(team__league=self.team.league)
sorted_player = sorted(players_to_sort, key=lambda player: player.point_total() )