Add a method to refresh Product stock

src/modules/inventory/models.py

@@ -2,6 +2,18 @@ from django.db import models
 
 
 class Product(models.Model):
+    # https://git.disroot.org/nsukami/interview/src/branch/feat-1/src/modules/inventory/tests.py#L59
     description = models.CharField(max_length=200)
     unit_price = models.FloatField()
     stock = models.IntegerField()
+
+    # https://git.disroot.org/nsukami/interview/src/branch/feat-1/src/modules/orders/tests.py#L111
+    # a product stock should be refreshed after an order is made
+    def refresh_from_db(self):
+        from modules.orders.models import OrderItem
+
+        # self.stock = self.stock - sum((oi.quantity for oi in self.orderitem_set.all()))
+        self.stock = self.stock - sum(
+            oi.quantity for oi in OrderItem.objects.filter(id=self.id)
+        )
+        self.save()

src/modules/inventory/views.py

@@ -9,6 +9,8 @@ class ProductSerializer(serializers.ModelSerializer):
         fields = "__all__"
 
 
+# https://git.disroot.org/nsukami/interview/src/branch/feat-1/src/modules/inventory/tests.py#L17
+# a product can be created, updated, listed but not deleted
 class ProductsViewSet(
     mixins.CreateModelMixin,
     mixins.ListModelMixin,