How do I display the data in belongs_to model? - ruby-on-rails

Question

I'd like to display "code" in comments model on "_article.html.erb". How should I modify following sources?
.schema articles
CREATE TABLE "articles" (
"id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
"content" varchar(255),
"user_id" integer,
"comment_id" integer,
"created_at" datetime,
"updated_at" datetime);
.schema comments
CREATE TABLE "comments" (
"id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
"code" integer,
"created_at" datetime,
"updated_at" datetime);
article.rb
class Article < ActiveRecord::Base
belongs_to :user
belongs_to :comment
end
comment.rb
class Comment < ActiveRecord::Base
has_many :articles
end
users/show.html.erb
<%= render #articles %>
articles/_article.html.erb
<li>
<%= article.comment.code %>
<span class="content"><%= article.content %></span>
by <%= article.user.name %>
</li>
users_controller.rb
class UsersController < ApplicationController
def index
#users = User.paginate(page: params[:page])
end
def show
#user = User.find(params[:id])
#articles = #user.articles.paginate(page: params[:page])
end
The following error appears on my screen after adding <%= article.comment.code %> in articles/_article.html.erb.
NoMethodError in Users#show
Showing e:/....../app/views/articles/_article.html.erb where line #2 raised:
undefined method `code' for nil:NilClass
Extracted source (around line #2):
1 <li>
2 <%= article.comment.code %>
3 <span class="content"><%= article.content %></span>
4 by <%= article.user.name %>
Trace of template inclusion: app/views/users/show.html.erb
app/views/articles/_article.html.erb:2:in `_app_views_articles__article_html_erb__849237918_32363016'
app/views/users/show.html.erb:7:in `_app_views_users_show_html_erb__1073019711_34316652'
Request
Parameters:
{"id"=>"1"}
And Full Trace is as follows;
app/views/articles/_article.html.erb:2:in `_app_views_articles__article_html_erb__849237918_32363016'
actionpack (4.0.4) lib/action_view/template.rb:143:in `block in render'
activesupport (4.0.4) lib/active_support/notifications.rb:161:in `instrument'
actionpack (4.0.4) lib/action_view/template.rb:141:in `render'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:399:in `block in collection_with_template'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:395:in `map'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:395:in `collection_with_template'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:291:in `render_collection'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:275:in `block in render'
actionpack (4.0.4) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.4) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (4.0.4) lib/action_view/renderer/partial_renderer.rb:274:in `render'
actionpack (4.0.4) lib/action_view/renderer/renderer.rb:47:in `render_partial'
actionpack (4.0.4) lib/action_view/helpers/rendering_helper.rb:27:in `render'
app/views/users/show.html.erb:7:in `_app_views_users_show_html_erb__1073019711_34316652'
actionpack (4.0.4) lib/action_view/template.rb:143:in `block in render'
activesupport (4.0.4) lib/active_support/notifications.rb:161:in `instrument'
actionpack (4.0.4) lib/action_view/template.rb:141:in `render'
actionpack (4.0.4) lib/action_view/renderer/template_renderer.rb:49:in `block (2 levels) in render_template'
actionpack (4.0.4) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.4) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (4.0.4) lib/action_view/renderer/template_renderer.rb:48:in `block in render_template'
actionpack (4.0.4) lib/action_view/renderer/template_renderer.rb:56:in `render_with_layout'
actionpack (4.0.4) lib/action_view/renderer/template_renderer.rb:47:in `render_template'
actionpack (4.0.4) lib/action_view/renderer/template_renderer.rb:17:in `render'
actionpack (4.0.4) lib/action_view/renderer/renderer.rb:42:in `render_template'
actionpack (4.0.4) lib/action_view/renderer/renderer.rb:23:in `render'
actionpack (4.0.4) lib/abstract_controller/rendering.rb:127:in `_render_template'
actionpack (4.0.4) lib/action_controller/metal/streaming.rb:219:in `_render_template'
actionpack (4.0.4) lib/abstract_controller/rendering.rb:120:in `render_to_body'
actionpack (4.0.4) lib/action_controller/metal/rendering.rb:33:in `render_to_body'
actionpack (4.0.4) lib/action_controller/metal/renderers.rb:26:in `render_to_body'
actionpack (4.0.4) lib/abstract_controller/rendering.rb:97:in `render'
actionpack (4.0.4) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:41:in `block (2 levels) in render'
activesupport (4.0.4) lib/active_support/core_ext/benchmark.rb:12:in `block in ms'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/benchmark.rb:295:in `realtime'
activesupport (4.0.4) lib/active_support/core_ext/benchmark.rb:12:in `ms'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:41:in `block in render'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:84:in `cleanup_view_runtime'
activerecord (4.0.4) lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:40:in `render'
actionpack (4.0.4) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (4.0.4) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (4.0.4) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.4) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.4) lib/active_support/callbacks.rb:433:in `_run__756630078__process_action__callbacks'
activesupport (4.0.4) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.4) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.4) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.4) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.4) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.4) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.0.4) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.4) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.4) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.4) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.4) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.4) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:80:in `call'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:80:in `dispatch'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:48:in `call'
actionpack (4.0.4) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.4) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.4) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.4) lib/action_dispatch/routing/route_set.rb:674: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 (4.0.4) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.4) 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 (4.0.4) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.4) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.4) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.4) lib/active_support/callbacks.rb:373:in `_run__522467988__call__callbacks'
activesupport (4.0.4) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.4) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.4) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.4) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.4) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.4) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.4) 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 (4.0.4) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.4) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
railties (4.0.4) lib/rails/engine.rb:511:in `call'
railties (4.0.4) 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'
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

You can use the relation between Article and Comment like this
<%= article.comment.code %>
to get the code of comment for the associated article.
The better way would be adding a delegate
class Article < ActiveRecord::Base
belongs_to :user
belongs_to :comment
delegate :code, to: 'comment', allow_nil: true
end
By doing so,you can simply call it as
<%= article.code%>
For more info,see this API

Answer 2

foreign_keys
Further to Pavan's answer, you'll be best understanding how ActiveRecord Associations work:
#app/models/comment.rb
Class Comment < ActiveRecord::Base
belongs_to :article
belongs_to :user
end
#app/models/article.rb
Class Article < ActiveRecord::Base
has_many :comments
end
This basically sets up a relational database connection, which will use foreign_keys to pull associative data on ActiveRecord objects:
#comments
id | user_id | article_id | message | created_at | updated_at
#articles
id | user_id | title | message | created_at | updated_at
--
Setup
I don't know why you've got article belongs_to comment - I presume the opposite would be true?
I would definitely look at how you want your ActiveRecord structure to work - the standard has_many association is pretty standard:
I'd personally set up the association like I described above, which will allow you to do the following:
#article = Article.find params[:id]
#article.comments.each do |comment|
comment.code
end