1.rb

    showing_request.showing_request_notifications.
      create!({
                recipient:         'listing_agent',
                notification_type: 'email',
                contact_name:      'John Smith',
                contact:           'john@example.com',
                token:             'token'
              },
              without_protection: true)

2.rb

showing_request.showing_request_notifications.create!({
                                                         recipient:         'listing_agent',
                                                         notification_type: 'email',
                                                         contact_name:      'John Smith',
                                                         contact:           'john@example.com',
                                                         token:             'token'
                                                       },
                                                       without_protection: true)

3.rb

showing_request.showing_request_notifications.create!({ recipient:         'listing_agent',
                                                            notification_type: 'email',
                                                            contact_name:      'John Smith',
                                                            contact:           'john@example.com',
                                                            token:             'token' },
                                                          without_protection: true)

4.rb

showing_request.showing_request_notifications.
      create!({ recipient:         'listing_agent',
                notification_type: 'email',
                contact_name:      'John Smith',
                contact:           'john@example.com',
                token:             'token' },
              without_protection: true)

notification_attributes = { recipient: 'listing_agent',
                            notification_type: 'email',
                            contact_name: 'John Smith',
                            contact: 'john@example.com',
                            token: 'token' }

showing_request.showing_request_notifications.create! notification_attributes,
                                                      without_protection: true

ну молодца!

Нельзя быстро добавить элемент ни в начало, ни в конец хеша

notification_attributes = { 
                            recipient: 'listing_agent',
                            notification_type: 'email',
                            contact_name: 'John Smith',
                            contact: 'john@example.com',
                            token: 'token' 
                          }

showing_request.showing_request_notifications.create! notification_attributes,
                                                      without_protection: true