Add created_at and updated_at to Product model

counter/migrations/0036_product_created_at_product_updated_at.py

@@ -0,0 +1,67 @@
+# Generated by Django 5.2.8 on 2026-02-10 15:40
+from operator import attrgetter
+
+import django.utils.timezone
+from django.db import migrations, models
+from django.db.migrations.state import StateApps
+from django.db.models import OuterRef, Subquery
+
+from counter.models import Selling
+
+
+def apply_product_history_dates(apps: StateApps, schema_editor):
+    """Approximate a posteriori the value of created_at and updated_at."""
+    Product = apps.get_model("counter", "Product")
+    sales_subquery = Selling.objects.filter(product=OuterRef("pk")).values("date")
+
+    # for products that have an associated sale, we set the creation date
+    # to the one of the first sale, and the update date to the one of the last sale
+    products = list(
+        Product.objects.exclude(sellings=None)
+        .annotate(
+            new_created_at=Subquery(sales_subquery.order_by("date")[:1]),
+            new_updated_at=Subquery(sales_subquery.order_by("-date")[:1]),
+        )
+        .only("id")
+    )
+    for product in products:
+        product.created_at = product.new_created_at
+        product.updated_at = product.new_updated_at
+
+    # For the remaining products (those without sale),
+    # they are given the creation and update date of the previous product having sales.
+    products_without_sale = list(Product.objects.filter(sellings=None).only("id"))
+    for product in products_without_sale:
+        previous_product = max(
+            (p for p in products if p.id < product.id), key=attrgetter("id")
+        )
+        product.created_at = previous_product.created_at
+        product.updated_at = previous_product.updated_at
+    products.extend(products_without_sale)
+
+    Product.objects.bulk_update(products, fields=["created_at", "updated_at"])
+
+
+class Migration(migrations.Migration):
+    dependencies = [("counter", "0035_remove_selling_is_validated_and_more")]
+
+    operations = [
+        migrations.AddField(
+            model_name="product",
+            name="created_at",
+            field=models.DateTimeField(
+                auto_now_add=True,
+                default=django.utils.timezone.now,
+                verbose_name="created at",
+            ),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name="product",
+            name="updated_at",
+            field=models.DateTimeField(auto_now=True, verbose_name="updated at"),
+        ),
+        migrations.RunPython(
+            apply_product_history_dates, reverse_code=migrations.RunPython.noop
+        ),
+    ]