feat: make student card unique per user

counter/migrations/0026_alter_studentcard_customer.py

@@ -0,0 +1,53 @@
+# Generated by Django 4.2.17 on 2024-12-08 13:30
+from operator import attrgetter
+
+import django.db.models.deletion
+from django.db import migrations, models
+from django.db.migrations.state import StateApps
+from django.db.models import Count
+
+
+def delete_duplicates(apps: StateApps, schema_editor):
+    """Delete cards of users with more than one student cards.
+
+    For all users who have more than one registered student card, all
+    the cards except the last one are deleted.
+    """
+    Customer = apps.get_model("counter", "Customer")
+    StudentCard = apps.get_model("counter", "StudentCard")
+    customers = (
+        Customer.objects.annotate(nb_cards=Count("student_cards"))
+        .filter(nb_cards__gt=1)
+        .prefetch_related("student_cards")
+    )
+    to_delete = [
+        card.id
+        for customer in customers
+        for card in sorted(customer.student_cards.all(), key=attrgetter("id"))[:-1]
+    ]
+    StudentCard.objects.filter(id__in=to_delete).delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [("counter", "0025_remove_product_parent_product_and_more")]
+
+    operations = [
+        migrations.RunPython(delete_duplicates, migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name="studentcard",
+            name="customer",
+            field=models.OneToOneField(
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="student_card",
+                to="counter.customer",
+                verbose_name="student card",
+            ),
+        ),
+        migrations.AlterModelOptions(
+            name="studentcard",
+            options={
+                "verbose_name": "student card",
+                "verbose_name_plural": "student cards",
+            },
+        ),
+    ]