add products relation in product's category

app/models/product.rb

@@ -7,4 +7,6 @@ class Product < ApplicationRecord
   has_and_belongs_to_many :machines
 
   validates_numericality_of :amount, greater_than: 0, allow_nil: true
+
+  scope :active, -> { where(is_active: true) }
 end

app/models/product_category.rb

@@ -8,5 +8,7 @@ class ProductCategory < ApplicationRecord
   belongs_to :parent, class_name: 'ProductCategory'
   has_many :children, class_name: 'ProductCategory', foreign_key: :parent_id
 
+  has_many :products
+
   acts_as_list scope: :parent, top_of_list: 0
 end