Rails/Pundit ArgumentError - ruby-on-rails

Question

In an exercise, I'm trying to create authorization such that a user needs to be either the post's owner or the general administrator, on top of being present and logged-in to update a post. I am trying to implement a pundit policy (using Devise for authentication).
The PostController Class:
class PostsController < ApplicationController
...
def edit
#post = Post.find(params[:id])
authorize #post
end
...
end
The ApplicationPolicy Class:
class ApplicationPolicy
attr_reader :user, :record
def initialize(user, record)
#user = user
#record = record
end
...
def update?
user.present? && (record.user == user || user.role?(:admin))
end
def edit?
update?
end
def destroy?
update?
end
...
end
* The User model* :
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable, :confirmable
has_many :posts
def role?(base_role)
role == base_role.to_s
end
end
I got stuck with the Argument Error: wrong number of arguments (2 for 1). My understanding is that the policy method is part of the Pundit module, and it initializes and returns a new policy object with the given record and current_user as the implicit user. Can someone help me shed a light into this issue?
ERROR MESSAGE:
Showing /home/vagrant/code/bloccit/app/views/posts/show.html.erb where line #3 raised:
<h1><%= #post.title %></h1>
<% if policy(#post).edit? %> #This is the line where the error is raised.
<%= link_to "Edit", edit_post_path(#post), class: 'btn btn-success' %>
<% end %>
wrong number of arguments (2 for 1)
Full error trace :
activerecord (4.0.10) lib/active_record/attribute_methods/query.rb:35:in `attribute?'
activemodel (4.0.10) lib/active_model/attribute_methods.rb:383:in `role?'
app/policies/application_policy.rb:26:in `update?'
app/policies/application_policy.rb:30:in `edit?'
app/views/posts/show.html.erb:3:in `_app_views_posts_show_html_erb__322214668_90107450'
actionpack (4.0.10) lib/action_view/template.rb:143:in `block in render'
activesupport (4.0.10) lib/active_support/notifications.rb:161:in `instrument'
actionpack (4.0.10) lib/action_view/template.rb:141:in `render'
actionpack (4.0.10) lib/action_view/renderer/template_renderer.rb:49:in `block (2 levels) in render_template'
actionpack (4.0.10) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.10) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.10) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (4.0.10) lib/action_view/renderer/template_renderer.rb:48:in `block in render_template'
actionpack (4.0.10) lib/action_view/renderer/template_renderer.rb:56:in `render_with_layout'
actionpack (4.0.10) lib/action_view/renderer/template_renderer.rb:47:in `render_template'
actionpack (4.0.10) lib/action_view/renderer/template_renderer.rb:17:in `render'
actionpack (4.0.10) lib/action_view/renderer/renderer.rb:42:in `render_template'
actionpack (4.0.10) lib/action_view/renderer/renderer.rb:23:in `render'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:127:in `_render_template'
actionpack (4.0.10) lib/action_controller/metal/streaming.rb:219:in `_render_template'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:120:in `render_to_body'
actionpack (4.0.10) lib/action_controller/metal/rendering.rb:33:in `render_to_body'
actionpack (4.0.10) lib/action_controller/metal/renderers.rb:26:in `render_to_body'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:97:in `render'
actionpack (4.0.10) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:41:in `block (2 levels) in render'
activesupport (4.0.10) lib/active_support/core_ext/benchmark.rb:12:in `block in ms'
/home/vagrant/.rvm/rubies/ruby-2.0.0-p576/lib/ruby/2.0.0/benchmark.rb:296:in `realtime'
activesupport (4.0.10) lib/active_support/core_ext/benchmark.rb:12:in `ms'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:41:in `block in render'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:84:in `cleanup_view_runtime'
activerecord (4.0.10) lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:40:in `render'
actionpack (4.0.10) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (4.0.10) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.10) lib/active_support/callbacks.rb:413:in `_run__423379461__process_action__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.10) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.0.10) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.10) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:50:in `call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:676:in `call'
warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
warden (1.2.3) lib/warden/manager.rb:34:in `catch'
warden (1.2.3) lib/warden/manager.rb:34:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:25:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.10) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.10) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.10) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.10) lib/active_support/callbacks.rb:373:in `_run__474745028__call__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.10) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.10) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
railties (4.0.10) lib/rails/engine.rb:511:in `call'
railties (4.0.10) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/home/vagrant/.rvm/rubies/ruby-2.0.0-p576/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/vagrant/.rvm/rubies/ruby-2.0.0-p576/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/vagrant/.rvm/rubies/ruby-2.0.0-p576/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

Answer 1

The first 2-3 lines of the error trace tell us the problem is in ApplicationPolicy#update? and User#role?:
activerecord (4.0.10) lib/active_record/attribute_methods/query.rb:35:in attribute?'
activemodel (4.0.10) lib/active_model/attribute_methods.rb:383:in role?'
app/policies/application_policy.rb:26:in update?'
Looking at the code in question:
class ApplicationPolicy
...
def update?
user.present? && (record.user == user || user.role?(:admin))
end
...
end
Here's a few things to try:
Check User has a role? method defined on it.
Check User#role? is being found and called. Insert logging or a raise "In User#role?" statement into the method to be certain.
Ensure db migrations have run on development and test environments by running the rake db:migrate and rake db:migrate RAILS_ENV=test tasks.
Restart the server rails s