Django-Filter over Managers

Question

I've been stuck in this for several weeks now and I believe the answer is super simple but somehow I can't find it anywhere online. Which makes me think I'm going about it totally wrong.

All I want to do is be able to filter my stats such as the get_largest_winning_trade function based on the django-filter package. Where am I going wrong? As a side note get_largest_winning_trade is showing the largest winning trade in the Trade Model but it is not being filtered for my criteria. Such as "user".

managers.py

from django.db import models

class TradeQuerySet(models.QuerySet):

    def get_users_trades(self, username):
        return self.filter(user__username=username)

class TradeManager(models.Manager):

    def get_queryset(self):
        return TradeQuerySet(self.model, using=self._db)

    def get_users_trades(self, username):
        return self.get_queryset().get_users_trades(username)

    def get_largest_winning_trade(self):
        return max([t.profit_loss_value_fees for t in self.all()])

views.py

class StatsView1(LoginRequiredMixin, ListView):
    model = Trade
    template_name = 'dashboard/stats1.html'

    def get_context_data(self, **kwargs):
        filter = StatsFilter1(self.request.GET, queryset=self.get_queryset())
        context = super().get_context_data(**kwargs)
        context['filter'] = filter
        context['get_largest_winning_trade'] = Trade.objects.get_largest_winning_trade
        return context

stats.html (testing)

        filter.qs.get_largest_winning_trade: {{ filter.qs.get_largest_winning_trade }} <br>
        Trade.get_largest_winning_trade: {{ Trade.get_largest_winning_trade }} <br>
        trade.get_largest_winning_trade: {{ trade.get_largest_winning_trade }} <br>
        get_largest_winning_trade: {{ get_largest_winning_trade }} <br>  # works but not with filter

---

Additional Requested Information

Shared the class, it's quite long so I tried to reduce it to what is most helpful. Please let me know if there's anything else.

models.py

class Trade(models.Model):
    class Meta:
        verbose_name = "Trade"
        verbose_name_plural = "Trades"
     ...

     user = models.ForeignKey(User, on_delete=models.CASCADE, blank=True)
     status = models.CharField(max_length=2, choices=STATUS_CHOICES, default='cl')
     type = models.CharField(max_length=5, choices=TYPE_CHOICES, default=LONG)
     broker = models.ForeignKey(Broker, on_delete=models.CASCADE, blank=True, null=True)
     asset = models.ForeignKey(Asset, default=DEFAULT_ASSET_ID, on_delete=models.CASCADE, null=True)
     #AUTOMATED FIELDS
     profit_loss_value_fees = models.FloatField(null=True)
     objects = TradeManager()
     ...

     def save(self):
         ...
         self.profit_loss_value_fees = self.get_profit_loss_value_fees()
         return super(Trade, self).save()

     ...

Answer 1

Probably you can do something like this using qs property:

def get_context_data(self, **kwargs):
    filter = StatsFilter1(self.request.GET, queryset=self.get_queryset())
    context = super().get_context_data(**kwargs)
    context['filter'] = filter
    context['get_largest_winning_trade'] = filter.qs.get_largest_winning_trade
    return context

Update

I think rather than doing it manager, you can do the calculation here with aggregation. Like this:

from django.db.models import Max
...

context['get_largest_winning_trade'] = filter.qs.aggregate(max_value=Max('profit_loss_value_fees'))['max_value']

Reason for using aggregation is to reduce DB hits, because your manager method will hit database multiple times during loop iteration.