2 files changed, 29 insertions, 0 deletions
diff --git a/pyblackbird_cc/payments/models.py b/pyblackbird_cc/payments/models.py
index 81bb1c8..b947a22 100644
--- a/pyblackbird_cc/payments/models.py
+++ b/pyblackbird_cc/payments/models.py
@@ -1,4 +1,5 @@
 from django.conf import settings
+from django.core.exceptions import ValidationError
 from django.db import models
 
 from pyblackbird_cc.resources.models import Resource
@@ -27,6 +28,8 @@ class ShoppingCart(models.Model):
         return f"Shopping Cart for {self.user.username}"
 
     def add_resource(self, resource: Resource):
+        if CartItem.objects.filter(cart=self, resource=resource).exists():
+            raise ValidationError(f"{resource.name} is already in your shopping cart.")
         item, created = CartItem.objects.get_or_create(
             cart=self,
             resource=resource,
diff --git a/pyblackbird_cc/payments/tests/test_models.py b/pyblackbird_cc/payments/tests/test_models.py
index fd26fea..4dab6e3 100644
--- a/pyblackbird_cc/payments/tests/test_models.py
+++ b/pyblackbird_cc/payments/tests/test_models.py
@@ -1,3 +1,4 @@
+from django.core.exceptions import ValidationError
 import pytest
 from allauth.account.signals import user_signed_up
 from django.contrib.auth import get_user_model
@@ -86,3 +87,28 @@ def test_cart_item_is_created_when_resource_is_added_to_cart(user_data, resource
     users_cart = ShoppingCart.objects.get(user=user)
     users_cart.add_resource(resource)
     assert users_cart.items.count() == 1  # type: ignore
+
+
+@pytest.mark.django_db
+def test_cannot_add_the_same_resource_to_cart_twice(user_data, resource):
+    user = User.objects.create_user(**user_data)  # type: ignore
+    request = RequestFactory().get("/")
+    user_signed_up.send(sender=user.__class__, request=request, user=user)
+    users_cart = ShoppingCart.objects.get(user=user)
+    users_cart.add_resource(resource)
+    assert users_cart.items.count() == 1  # type: ignore
+    with pytest.raises(ValidationError):
+        users_cart.add_resource(resource)
+
+
+@pytest.mark.django_db
+def test_can_add_multiple_different_items_to_cart(user_data, resources):
+    user = User.objects.create_user(**user_data)  # type: ignore
+    request = RequestFactory().get("/")
+    user_signed_up.send(sender=user.__class__, request=request, user=user)
+    users_cart = ShoppingCart.objects.get(user=user)
+    users_cart.add_resource(resources[0])
+    users_cart.add_resource(resources[1])
+    users_cart.add_resource(resources[2])
+    users_cart.add_resource(resources[3])
+    assert users_cart.items.count() == 4  # type: ignore