subject.rb

#The model section:

class Subject < ActiveRecord::Base
  
validates :name, :sex, :initial, :phone, :born_on, presence: true
validates :initial, :email, :phone, uniqueness: true, unless: :skip_unique_validation
validates :phone, format: { with: /\d/,
    message: "allows only numbers" }

attr_accessor :skip_unique_validation
    
end

#The controller section:

   def update
     @subject.skip_unique_validation = true
     @subject = Subject.find(params[:id])
     
     if @subject.update(subject_params)
       redirect_to @subject
     else
       render 'edit'
     end
   end