Custom Validator for JSON in Rails

my_object.rb

class MyObject < ActiveRecord::Base  
  class JsonValidator < ActiveModel::EachValidator
    def initialize(options)
      options.reverse_merge!(:message => :invalid)
      super(options)
    end

    def validate_each(record, attribute_before_typecast, value)
      attribute = attribute_before_typecast.to_s.sub('_before_type_cast', '')
      value = value.strip if value.is_a?(String)
      JSON.parse(value)
    rescue JSON::ParserError, TypeError => exception
      record.errors.add(attribute, options[:message], exception_message: exception.message)
    end
  end

  validates :my_json_field_before_type_cast, presence: true, json: true
end