1

我正在编写一个联赛系统，我想显示每个赛季的球员排名，按每个球员在该赛季累积的积分排序。

到目前为止，我设法使用类似于以下的代码来做到这一点：

class Player(models.Model):
    name = models.CharField(max_length=100)


class Season(models.Model):
    name = models.CharField(max_length=100)
    start_date = models.DateField()
    end_date = models.DateField()
    players = models.ManyToManyField(Player)

    def get_player_rank(self, player):
        return player.matchresult_set.filter(season=self).aggregate(points=Sum('points'))['points']

    def get_ranks(self):
        ranks = [(player, self.get_player_rank(player)) for player in self.players.all()]
        ranks.sort(key=lambda tup: tup[1])
        return ranks


class Match(models.Model):
    date = models.DateField()
    players = models.ManyToManyField(Player, through='MatchResult')
    season = models.ForeignKey(Season)


class MatchResult(models.Model):
    player = models.ForeignKey(Player)
    match = models.ForeignKey(Match)
    points = models.IntegerField()

我认为同样可以通过更简单的聚合来实现，但我就是无法正确使用 annotate()。

我试过这个，但它只是总结了整个赛季的所有点：

class Season(models.Model):    
    def get_ranks(self):
        return self.players.annotate(points=Sum('matchresult__points')).order_by('-points')

我错过了什么？我猜如果 .extra() 会导致可移植代码，则可以使用它。

4

2 回答 2

2

这将返回可用的结果：

Season.objects.values('name','match__matchresult__player__username').annotate(points=Sum('match__matchresult__points')).distinct()

我还需要实现 SumWithDefault 以摆脱 NULL：

from django.db.models.sql.aggregates import Aggregate
from django.db.models import Aggregate as Ag

class SumWithDefaultSQL(Aggregate):
    def __init__(self, col, default=None, **extra):
        super(SumWithDefaultSQL, self).__init__(col, default=default, **extra)
        self.sql_function = 'SUM'
        if default is not None:
            self.sql_template = 'COALESCE(%(function)s(%(field)s), %(default)s)'


class SumWithDefault(Ag):
    name = 'Sum'

    def add_to_query(self, query, alias, col, source, is_summary):
        aggregate = SumWithDefaultSQL(col, source=source, is_summary=is_summary, **self.extra)
        query.aggregates[alias] = aggregate

最终查询：

Season.objects.values('name','match__matchresult__player__username').annotate(points=SumWithDefault('match__matchresult__points', default=0)).distinct().order_by('-points')
于 2014-02-04T07:15:00.577 回答
-1

Django 的 ORM 并没有涵盖所有用例。

您可以将聚合存储在单独的模型中或回退到原始 SQL。

于 2014-02-03T13:46:44.167 回答