feat(prices): new querysets to calculate min, max & average (#452)

open_prices/prices/models.py

@@ -2,7 +2,8 @@
 
 from django.core.validators import MinValueValidator, ValidationError
 from django.db import models
-from django.db.models import F, signals
+from django.db.models import Avg, Count, F, Max, Min, signals
+from django.db.models.functions import Cast
 from django.dispatch import receiver
 from django.utils import timezone
 from openfoodfacts.taxonomy import get_taxonomy
@@ -17,6 +18,36 @@
 from open_prices.users.models import User
 
 
+class PriceQuerySet(models.QuerySet):
+    def exclude_discounted(self):
+        return self.filter(price_is_discounted=False)
+
+    def calculate_min(self):
+        return self.aggregate(Min("price"))["price__min"]
+
+    def calculate_max(self):
+        return self.aggregate(Max("price"))["price__max"]
+
+    def calculate_avg(self):
+        return self.aggregate(
+            price__avg=Cast(
+                Avg("price"),
+                output_field=models.DecimalField(max_digits=10, decimal_places=2),
+            )
+        )["price__avg"]
+
+    def calculate_stats(self):
+        return self.aggregate(
+            price__count=Count("pk"),
+            price__min=Min("price"),
+            price__max=Max("price"),
+            price__avg=Cast(
+                Avg("price"),
+                output_field=models.DecimalField(max_digits=10, decimal_places=2),
+            ),
+        )
+
+
 class Price(models.Model):
     UPDATE_FIELDS = [
         "price",
@@ -108,6 +139,8 @@ class Price(models.Model):
     created = models.DateTimeField(default=timezone.now)
     updated = models.DateTimeField(auto_now=True)
 
+    objects = models.Manager.from_queryset(PriceQuerySet)()
+
     class Meta:
         # managed = False
         db_table = "prices"

open_prices/prices/tests.py

@@ -1,3 +1,5 @@
+from decimal import Decimal
+
 from django.core.exceptions import ValidationError
 from django.test import TestCase
 
@@ -6,6 +8,7 @@
 from open_prices.locations.models import Location
 from open_prices.prices import constants as price_constants
 from open_prices.prices.factories import PriceFactory
+from open_prices.prices.models import Price
 from open_prices.products.factories import ProductFactory
 from open_prices.products.models import Product
 from open_prices.proofs import constants as proof_constants
@@ -15,6 +18,50 @@
 from open_prices.users.models import User
 
 
+class PriceQuerySetTest(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        PriceFactory(price=5, price_is_discounted=True, price_without_discount=10)
+        PriceFactory(price=8)
+        PriceFactory(price=10)
+
+    def test_exclude_discounted(self):
+        self.assertEqual(Price.objects.count(), 3)
+        self.assertEqual(Price.objects.exclude_discounted().count(), 2)
+
+    def test_min(self):
+        self.assertEqual(Price.objects.calculate_min(), 5)
+        self.assertEqual(Price.objects.exclude_discounted().calculate_min(), 8)
+
+    def test_max(self):
+        self.assertEqual(Price.objects.calculate_max(), 10)
+        self.assertEqual(Price.objects.exclude_discounted().calculate_max(), 10)
+
+    def test_avg(self):
+        self.assertEqual(Price.objects.calculate_avg(), Decimal("7.67"))
+        self.assertEqual(Price.objects.exclude_discounted().calculate_avg(), 9)
+
+    def test_calculate_stats(self):
+        self.assertEqual(
+            Price.objects.calculate_stats(),
+            {
+                "price__count": 3,
+                "price__min": 5,
+                "price__max": 10,
+                "price__avg": Decimal("7.67"),
+            },
+        )
+        self.assertEqual(
+            Price.objects.exclude_discounted().calculate_stats(),
+            {
+                "price__count": 2,
+                "price__min": 8,
+                "price__max": 10,
+                "price__avg": 9,
+            },
+        )
+
+
 class PriceModelSaveTest(TestCase):
     @classmethod
     def setUpTestData(cls):