1 files changed, 9 insertions, 0 deletions
diff --git a/app/models/product_cart.rb b/app/models/product_cart.rb
index 10d4a4c..eb9cf9f 100644
--- a/app/models/product_cart.rb
+++ b/app/models/product_cart.rb
@@ -5,4 +5,13 @@
 class ProductCart < ApplicationRecord
   belongs_to :cart
   belongs_to :product
+
+  validates :quantity, presence: true, comparison: { greater_than: 0 }
+  validate :sole_product_in_cart
+
+  def sole_product_in_cart
+    return if cart.products.find_by(id: product_id).nil?
+
+    errors.add(:product_id, "cart already has product with id #{product_id}")
+  end
 end