Added Token field for physical_ticket

Added token field in physical_ticket model. This token will also be stored in the qr code and will uniqely identify the ticket.

app/models/physical_ticket.rb

@@ -4,4 +4,19 @@ class PhysicalTicket < ActiveRecord::Base
   has_one :conference, through: :ticket_purchase
   has_one :user, through: :ticket_purchase
   has_many :ticket_scannings
+
+  before_create :set_token
+
+  private
+
+  def set_token
+    self.token = generate_token
+  end
+
+  def generate_token
+    loop do
+      token = SecureRandom.hex(10)
+      break token unless PhysicalTicket.exists?(token: token)
+    end
+  end
 end