ruby on rails - No implicit conversion of String into Integer for import CSV file -

when import csv file different attributes: parent , student. error message: no implicit conversion of string integer. how can import parent’s attributes within student attributes. appreciated.

class student < activerecord::base     belongs_to :parent    delegate :email,:name,:phone_number,to: :parent, allow_nil: true  def self.to_csv       attributes = %w{parent_id email phone_number first_name last_name  age workshop interest registration_date email   }             csv.generate(headers: true) |csv|               csv << attributes               all.each |script|               csv << attributes.map{ |attr| script.send(attr) }               end             end          end     def self.import(file)       spreadsheet = open_spreadsheet(file)       header=spreadsheet.row(1)        (2..spreadsheet.last_row).each |i|          row = hash[[header,spreadsheet.row(i)].transpose]        spreadsheet.each |row|       student = find_by_id(row["id"])|| new       parent = student.parent || student.build_parent       student.attributes = row.slice(*student_attributes)       parent.attributes = row.slice(*parent_attributes)       student.save!       parent.save!     end   end end    def self.open_spreadsheet(file)     case file.extname(file.original_filename)     when ".csv" roo::csv.new(file.path)     when ".xls" roo::csv.new(file.path)     when ".xlsx" roo::csv.new(file.path)     else raise "unknown file type: #{file.original_filename}"     end   end end 

student controller:

def import   student.import(params[:file])   redirect_to root_url, notice: "student imported."   end end 

view folder:

<h2>import students</h2>  <%= form_tag import_students_path, multipart: true %>   <%= file_field_tag :file %>   <%= submit_tag "import" %> <% end %> 

here full trace error:

app/models/student.rb:85:in `[]' app/models/student.rb:85:in `block (2 levels) in import' roo (2.3.2) lib/roo/base.rb:360:in `block in each' roo (2.3.2) lib/roo/base.rb:359:in `upto' roo (2.3.2) lib/roo/base.rb:359:in `each' app/models/student.rb:84:in `block in import' activesupport (4.2.1) lib/active_support/core_ext/range/each.rb:7:in `each' activesupport (4.2.1) lib/active_support/core_ext/range/each.rb:7:in `each_with_time_with_zone' app/models/student.rb:70:in `import' app/controllers/students_controller.rb:15:in `import' actionpack (4.2.1) lib/action_controller/metal/implicit_render.rb:4:in `send_action' actionpack (4.2.1) lib/abstract_controller/base.rb:198:in `process_action' actionpack (4.2.1) lib/action_controller/metal/rendering.rb:10:in `process_action' actionpack (4.2.1) lib/abstract_controller/callbacks.rb:20:in `block in process_action' activesupport (4.2.1) lib/active_support/callbacks.rb:117:in `call' activesupport (4.2.1) lib/active_support/callbacks.rb:117:in `call' activesupport (4.2.1) lib/active_support/callbacks.rb:555:in `block (2 levels) in compile' activesupport (4.2.1) lib/active_support/callbacks.rb:505:in `call' activesupport (4.2.1) lib/active_support/callbacks.rb:505:in `call' activesupport (4.2.1) lib/active_support/callbacks.rb:92:in `_run_callbacks' activesupport (4.2.1) lib/active_support/callbacks.rb:776:in `_run_process_action_callbacks' activesupport (4.2.1) lib/active_support/callbacks.rb:81:in `run_callbacks' actionpack (4.2.1) lib/abstract_controller/callbacks.rb:19:in `process_action' actionpack (4.2.1) lib/action_controller/metal/rescue.rb:29:in `process_action' actionpack (4.2.1) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action' activesupport (4.2.1) lib/active_support/notifications.rb:164:in `block in instrument' activesupport (4.2.1) lib/active_support/notifications/instrumenter.rb:20:in `instrument' activesupport (4.2.1) lib/active_support/notifications.rb:164:in `instrument' actionpack (4.2.1) lib/action_controller/metal/instrumentation.rb:30:in `process_action' actionpack (4.2.1) lib/action_controller/metal/params_wrapper.rb:250:in `process_action' activerecord (4.2.1) lib/active_record/railties/controller_runtime.rb:18:in `process_action' actionpack (4.2.1) lib/abstract_controller/base.rb:137:in `process' actionview (4.2.1) lib/action_view/rendering.rb:30:in `process' actionpack (4.2.1) lib/action_controller/metal.rb:196:in `dispatch' actionpack (4.2.1) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch' actionpack (4.2.1) lib/action_controller/metal.rb:237:in `block in action' actionpack (4.2.1) lib/action_dispatch/routing/route_set.rb:74:in `call' actionpack (4.2.1) lib/action_dispatch/routing/route_set.rb:74:in `dispatch' actionpack (4.2.1) lib/action_dispatch/routing/route_set.rb:43:in `serve' actionpack (4.2.1) lib/action_dispatch/journey/router.rb:43:in `block in serve' actionpack (4.2.1) lib/action_dispatch/journey/router.rb:30:in `each' actionpack (4.2.1) lib/action_dispatch/journey/router.rb:30:in `serve' actionpack (4.2.1) lib/action_dispatch/routing/route_set.rb:819:in `call' rack (1.6.4) lib/rack/etag.rb:24:in `call' rack (1.6.4) lib/rack/conditionalget.rb:38:in `call' rack (1.6.4) lib/rack/head.rb:13:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/params_parser.rb:27:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/flash.rb:260:in `call' rack (1.6.4) lib/rack/session/abstract/id.rb:225:in `context' rack (1.6.4) lib/rack/session/abstract/id.rb:220:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/cookies.rb:560:in `call' activerecord (4.2.1) lib/active_record/query_cache.rb:36:in `call' activerecord (4.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:649:in `call' activerecord (4.2.1) lib/active_record/migration.rb:378:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call' activesupport (4.2.1) lib/active_support/callbacks.rb:88:in `call' activesupport (4.2.1) lib/active_support/callbacks.rb:88:in `_run_callbacks' activesupport (4.2.1) lib/active_support/callbacks.rb:776:in `_run_call_callbacks' activesupport (4.2.1) lib/active_support/callbacks.rb:81:in `run_callbacks' actionpack (4.2.1) lib/action_dispatch/middleware/callbacks.rb:27:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/reloader.rb:73:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/remote_ip.rb:78:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call' web-console (2.3.0) lib/web_console/middleware.rb:20:in `block in call' web-console (2.3.0) lib/web_console/middleware.rb:18:in `catch' web-console (2.3.0) lib/web_console/middleware.rb:18:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call' railties (4.2.1) lib/rails/rack/logger.rb:38:in `call_app' railties (4.2.1) lib/rails/rack/logger.rb:20:in `block in call' activesupport (4.2.1) lib/active_support/tagged_logging.rb:68:in `block in tagged' activesupport (4.2.1) lib/active_support/tagged_logging.rb:26:in `tagged' activesupport (4.2.1) lib/active_support/tagged_logging.rb:68:in `tagged' railties (4.2.1) lib/rails/rack/logger.rb:20:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/request_id.rb:21:in `call' rack (1.6.4) lib/rack/methodoverride.rb:22:in `call' rack (1.6.4) lib/rack/runtime.rb:18:in `call' activesupport (4.2.1) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call' rack (1.6.4) lib/rack/lock.rb:17:in `call' actionpack (4.2.1) lib/action_dispatch/middleware/static.rb:113:in `call' rack (1.6.4) lib/rack/sendfile.rb:113:in `call' railties (4.2.1) lib/rails/engine.rb:518:in `call' railties (4.2.1) lib/rails/application.rb:164:in `call' rack (1.6.4) lib/rack/lock.rb:17:in `call' rack (1.6.4) lib/rack/content_length.rb:15:in `call' rack (1.6.4) lib/rack/handler/webrick.rb:88:in `service' /home/vagrant/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service' /home/vagrant/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run' /home/vagrant/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'