Rails: after_add giving error wrong number of arguments (1 for 0)

Question

I have the following models:

class Review < ActiveRecord::Base
  attr_accessible :votes_sum

  has_many :votes, :as => :voteable,
    :after_add => :sum_votes,
    :after_remove => :sum_votes

  def sum_votes
    update_attribute(:votes_sum, votes.sum(:value))
  end
end

And:

class Vote < ActiveRecord::Base
  attr_accessible :value

  belongs_to :voteable, :polymorphic => true
end

When I try creating a vote, I get this error:

wrong number of arguments (1 for 0)

Which is triggered on line 13 of review.rb:

def sum_votes

Where is this argument coming from? When I call sum_votes, I'm not passing in an argument.

UPDATE:

The full stack trace:

app/models/review.rb:13:in `sum_votes'
activerecord (3.2.11) lib/active_record/associations/collection_association.rb:507:in `block in callback'
activerecord (3.2.11) lib/active_record/associations/collection_association.rb:504:in `each'
activerecord (3.2.11) lib/active_record/associations/collection_association.rb:504:in `callback'
activerecord (3.2.11) lib/active_record/associations/collection_association.rb:352:in `add_to_target'
activerecord (3.2.11) lib/active_record/associations/collection_association.rb:112:in `build'
C:in `build'
app/models/user.rb:251:in `build_vote'
app/controllers/votes_controller.rb:9:in `create'
actionpack (3.2.11) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.11) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.11) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.11) lib/active_support/callbacks.rb:425:in `_run__943985968__process_action__580999264__callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.11) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.11) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.11) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.11) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.11) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.11) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.11) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.11) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.11) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:601:in `call'
warden (1.2.1) lib/warden/manager.rb:35:in `block in call'
warden (1.2.1) lib/warden/manager.rb:34:in `catch'
warden (1.2.1) lib/warden/manager.rb:34:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.4) lib/rack/etag.rb:23:in `call'
rack (1.4.4) lib/rack/conditionalget.rb:35:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.4) lib/rack/session/abstract/id.rb:210:in `context'
rack (1.4.4) lib/rack/session/abstract/id.rb:205:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/cookies.rb:341:in `call'
activerecord (3.2.11) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `_run__942047474__call__281283767__callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.11) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.11) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.11) lib/rails/rack/logger.rb:32:in `call_app'
railties (3.2.11) lib/rails/rack/logger.rb:16:in `block in call'
activesupport (3.2.11) lib/active_support/tagged_logging.rb:22:in `tagged'
railties (3.2.11) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.4) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.4) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.11) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.4) lib/rack/lock.rb:15:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.11) lib/rails/engine.rb:479:in `call'
railties (3.2.11) lib/rails/application.rb:223:in `call'
rack (1.4.4) lib/rack/content_length.rb:14:in `call'
railties (3.2.11) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.4) lib/rack/handler/webrick.rb:59:in `service'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

Answer 1

Mongoid passes the document created in the associated collection to the callback method, see here: Relation callbacks

You will have to change the signature of your method to receive that document, even if you don't use it (I improved the method too, by using inc):

def sum_votes(vote)
  inc(:votes_sum, 1)
end