feat: ProductFormula model

counter/migrations/0036_productformula.py

@@ -0,0 +1,43 @@
+# Generated by Django 5.2.8 on 2025-11-26 11:34
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [("counter", "0035_remove_selling_is_validated_and_more")]
+
+    operations = [
+        migrations.CreateModel(
+            name="ProductFormula",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "products",
+                    models.ManyToManyField(
+                        help_text="The products that constitute this formula.",
+                        related_name="formulas",
+                        to="counter.product",
+                        verbose_name="products",
+                    ),
+                ),
+                (
+                    "result",
+                    models.OneToOneField(
+                        help_text="The formula product.",
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to="counter.product",
+                        verbose_name="result product",
+                    ),
+                ),
+            ],
+        ),
+    ]

counter/models.py

@@ -455,6 +455,24 @@ class Product(models.Model):
         return self.selling_price - self.purchase_price
 
 
+class ProductFormula(models.Model):
+    products = models.ManyToManyField(
+        Product,
+        related_name="formulas",
+        verbose_name=_("products"),
+        help_text=_("The products that constitute this formula."),
+    )
+    result = models.OneToOneField(
+        Product,
+        on_delete=models.CASCADE,
+        verbose_name=_("result product"),
+        help_text=_("The product got with the formula."),
+    )
+
+    def __str__(self):
+        return self.result.name
+
+
 class CounterQuerySet(models.QuerySet):
     def annotate_has_barman(self, user: User) -> Self:
         """Annotate the queryset with the `user_is_barman` field.