update

pkg/cart/mutation_set_user_id.go

@@ -0,0 +1,14 @@
+package cart
+
+import (
+	"errors"
+	messages "git.tornberg.me/go-cart-actor/pkg/messages"
+)
+
+func SetUserId(grain *CartGrain, req *messages.SetUserId) error {
+	if req.UserId == "" {
+		return errors.New("user ID cannot be empty")
+	}
+	grain.userId = req.UserId
+	return nil
+}