custom primary key for transaction

app/models/sale_tax.rb

@@ -1,5 +1,10 @@
 class SaleTax < ApplicationRecord
 #primary key - need to be unique generated for multiple shops
-
+  before_create :generate_custom_id
   belongs_to :sale
+
+  private
+  def generate_custom_id
+    self.sale_tax_id = SeedGenerator.generate_id(self.class.name, "STI")
+  end
 end