Dry ORM

Code

Result

no cache

from django.db import models
from django.utils import timezone
import datetime

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

class Bale(models.Model):
    TIMESTAMP = models.DateTimeField()
    weight_kg = models.FloatField(default=0.0)

class BalingActivity(models.Model):
    COMPACTOR = models.ForeignKey(Compactor, on_delete=models.CASCADE)
    TIMESTAMP = models.DateTimeField()
    BALES = models.ManyToManyField(Bale)

def run():
    compactor = Compactor.objects.create(name='Compactor A')

now = timezone.now()
    bale_old = Bale.objects.create(TIMESTAMP=now - datetime.timedelta(hours=3), weight_kg=120.5)
    bale_mid = Bale.objects.create(TIMESTAMP=now - datetime.timedelta(hours=2), weight_kg=130.0)
    bale_new = Bale.objects.create(TIMESTAMP=now - datetime.timedelta(hours=1), weight_kg=125.0)

activity1 = BalingActivity.objects.create(COMPACTOR=compactor, TIMESTAMP=now - datetime.timedelta(days=1))
    activity2 = BalingActivity.objects.create(COMPACTOR=compactor, TIMESTAMP=now)

activity1.BALES.add(bale_old, bale_mid)
    activity2.BALES.add(bale_new)

# V1

prev_baling_activity_A = BalingActivity.objects.filter(COMPACTOR=compactor).order_by('TIMESTAMP').last()
    v1_bale = list(
        prev_baling_activity_A.BALES.through.objects
        .filter(balingactivity=prev_baling_activity_A)
        .select_related('bale')
        .order_by('-bale__TIMESTAMP')
    )[0].bale

# V2
    
    v2_bale = (
        BalingActivity.BALES.through.objects
        .filter(balingactivity__COMPACTOR=compactor)
        .select_related('bale')
        .order_by('balingactivity__TIMESTAMP', '-bale__TIMESTAMP')
        .last().bale
    )

assert v1_bale == v2_bale

Output

No output.

Queries

Queries Q (0)

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