diff --git a/rails_application/app/controllers/orders_controller.rb b/rails_application/app/controllers/orders_controller.rb
index 08bccd19..19001480 100644
--- a/rails_application/app/controllers/orders_controller.rb
+++ b/rails_application/app/controllers/orders_controller.rb
@@ -77,7 +77,7 @@ def add_item
 
     @order = Order.find(params[:id])
     @order.add_item(product)
-    Inventory::ProductService.new.decrement_stock_level(product.id)
+    Inventory::ProductService.new.decrement_stock_level(Inventory::DecreaseStockLevel.new(product_id: product.id))
     @order.save!
 
     redirect_to edit_order_path(params[:id])
@@ -87,7 +87,7 @@ def remove_item
     product = Product.find(params[:product_id])
     @order = Order.find(params[:id])
     @order.remove_item(product)
-    Inventory::ProductService.new.increment_stock_level(product.id)
+    Inventory::ProductService.new.increment_stock_level(Inventory::IncreaseStockLevel.new(product_id: product.id))
     @order.save!
 
     redirect_to edit_order_path(params[:id])
@@ -113,7 +113,7 @@ def expire
       .where(status: "Draft")
       .find_each do |order|
       order.order_items.each do |item|
-        Inventory::ProductService.new.increment_stock_level(item.product.id)
+        Inventory::ProductService.new.increment_stock_level(Inventory::IncreaseStockLevel.new(product_id: item.product_id))
       end
       order.status = "Expired"
       order.save!
diff --git a/rails_application/app/controllers/supplies_controller.rb b/rails_application/app/controllers/supplies_controller.rb
index 089a5378..956190f5 100644
--- a/rails_application/app/controllers/supplies_controller.rb
+++ b/rails_application/app/controllers/supplies_controller.rb
@@ -4,7 +4,7 @@ def new
   end
 
   def create
-    Inventory::ProductService.new.supply(params[:product_id].to_i, params[:quantity].to_i)
+    Inventory::ProductService.new.supply(Inventory::SupplyStockLevel.new(params[:product_id], params[:quantity]))
     redirect_to products_path, notice: "Stock level changed"
   end
 end
diff --git a/rails_application/app/models/inventory/decrease_stock_level.rb b/rails_application/app/models/inventory/decrease_stock_level.rb
new file mode 100644
index 00000000..d2c0e238
--- /dev/null
+++ b/rails_application/app/models/inventory/decrease_stock_level.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module Inventory
+  DecreaseStockLevel = Struct.new(:product_id)
+end
+
diff --git a/rails_application/app/models/inventory/increase_stock_level.rb b/rails_application/app/models/inventory/increase_stock_level.rb
new file mode 100644
index 00000000..75d9581b
--- /dev/null
+++ b/rails_application/app/models/inventory/increase_stock_level.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+module Inventory
+  IncreaseStockLevel = Struct.new(:product_id)
+end
diff --git a/rails_application/app/models/inventory/product_service.rb b/rails_application/app/models/inventory/product_service.rb
index d64424b8..e5c7866a 100644
--- a/rails_application/app/models/inventory/product_service.rb
+++ b/rails_application/app/models/inventory/product_service.rb
@@ -7,7 +7,8 @@ def initialize
       @repository = Infra::AggregateRootRepository.new(event_store)
     end
 
-    def decrement_stock_level(product_id)
+    def decrement_stock_level(command)
+      product_id = command.product_id
       ApplicationRecord.with_advisory_lock("change_stock_level_for_#{product_id}") do
         product = ::Product.find(product_id)
         product_stream = event_store.read.stream("Inventory::Product$#{product_id}").to_a
@@ -26,7 +27,8 @@ def decrement_stock_level(product_id)
       end
     end
 
-    def increment_stock_level(product_id)
+    def increment_stock_level(command)
+      product_id = command.product_id
       ApplicationRecord.with_advisory_lock("change_stock_level_for_#{product_id}") do
         product = ::Product.find(product_id)
         product_stream = event_store.read.stream("Inventory::Product$#{product_id}").to_a
@@ -45,7 +47,10 @@ def increment_stock_level(product_id)
       end
     end
 
-    def supply(product_id, quantity)
+    def supply(command)
+      product_id = command.product_id
+      quantity = command.quantity
+
       ApplicationRecord.with_advisory_lock("change_stock_level_for_#{product_id}") do
         product = ::Product.find(product_id)
         product.stock_level == nil ? product.stock_level = quantity : product.stock_level += quantity
diff --git a/rails_application/app/models/inventory/supply_stock_level.rb b/rails_application/app/models/inventory/supply_stock_level.rb
new file mode 100644
index 00000000..6464b556
--- /dev/null
+++ b/rails_application/app/models/inventory/supply_stock_level.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Inventory
+  SupplyStockLevel = Struct.new(:product_id, :quantity) do
+    def initialize(product_id, quantity)
+      super(product_id.to_i, quantity.to_i)
+    end
+  end
+end