インデックスアクションプレゼンターのメソッドを初期化

Question

Eventのインデックスアクションのプレゼンターにしたいと思います。

ここにその外観があります。そこプレゼンターとビューに追加以上のメソッドとの事であってもよいが、今の私はこの作業を取得することになるでしょう：

class EventPresenter 

    def initialize(events, template) 
    @events = events 
    @template = template 
    end 

    def h 
    @template 
    end 

    def event_title 
    h.link_to event.name, event_path(event) 
    end 
end 

index.html.erb：

<% present @events do |event_presenter| %> <tr> 
    <td><%= event_presenter.event_title %></td> 
<% end %> 

アプリケーションヘルパー：

module ApplicationHelper 
    def present(object, klass = nil) 
    klass ||= "#{object.class}Presenter".constantize 
    presenter = klass.new(object, self) 
    yield presenter if block_given? 
    presenter 
    end 
end 

events_controller：

def index 
    @events = Event.all.map{ |event| EventPresenter.new(event) } 
    # render json: @events 
    end 

今のところ、プレゼンターのinitializeメソッドでwrong number of arguments (1 for 2)エラーが発生します。私は、次のような、@eventsまたは@templateのいずれかを除去することにより、初期化に渡され取得されていない二つの物体のかを確認しようとしていた。

def initialize(template) 
    @template = template 
    end 

しかし、とapplication_helperのklass ||=ラインでどちらの場合も、アプリの改uninitialized constant ArrayPresenter、それはEventPresenter定数を探しているはずです。

フル・トレースは：

activesupport (5.0.0.beta3) lib/active_support/inflector/methods.rb:259:in `const_get' 
activesupport (5.0.0.beta3) lib/active_support/inflector/methods.rb:259:in `block in constantize' 
activesupport (5.0.0.beta3) lib/active_support/inflector/methods.rb:257:in `each' 
activesupport (5.0.0.beta3) lib/active_support/inflector/methods.rb:257:in `inject' 
activesupport (5.0.0.beta3) lib/active_support/inflector/methods.rb:257:in `constantize' 
activesupport (5.0.0.beta3) lib/active_support/core_ext/string/inflections.rb:66:in `constantize' 
app/helpers/application_helper.rb:3:in `present' 
app/views/events/index.html.erb:1:in `_app_views_events_index_html_erb__1682590753278671208_70298040094320' 
actionview (5.0.0.beta3) lib/action_view/template.rb:158:in `block in render' 
activesupport (5.0.0.beta3) lib/active_support/notifications.rb:166:in `instrument' 
actionview (5.0.0.beta3) lib/action_view/template.rb:348:in `instrument' 
actionview (5.0.0.beta3) lib/action_view/template.rb:156:in `render' 
actionview (5.0.0.beta3) lib/action_view/renderer/template_renderer.rb:54:in `block (2 levels) in render_template' 
actionview (5.0.0.beta3) lib/action_view/renderer/abstract_renderer.rb:42:in `block in instrument' 
activesupport (5.0.0.beta3) lib/active_support/notifications.rb:164:in `block in instrument' 
activesupport (5.0.0.beta3) lib/active_support/notifications/instrumenter.rb:21:in `instrument' 
activesupport (5.0.0.beta3) lib/active_support/notifications.rb:164:in `instrument' 
actionview (5.0.0.beta3) lib/action_view/renderer/abstract_renderer.rb:41:in `instrument' 
actionview (5.0.0.beta3) lib/action_view/renderer/template_renderer.rb:53:in `block in render_template' 
actionview (5.0.0.beta3) lib/action_view/renderer/template_renderer.rb:61:in `render_with_layout' 
actionview (5.0.0.beta3) lib/action_view/renderer/template_renderer.rb:52:in `render_template' 
actionview (5.0.0.beta3) lib/action_view/renderer/template_renderer.rb:14:in `render' 
actionview (5.0.0.beta3) lib/action_view/renderer/renderer.rb:42:in `render_template' 
actionview (5.0.0.beta3) lib/action_view/renderer/renderer.rb:23:in `render' 
actionview (5.0.0.beta3) lib/action_view/rendering.rb:103:in `_render_template' 
actionpack (5.0.0.beta3) lib/action_controller/metal/streaming.rb:217:in `_render_template' 
actionview (5.0.0.beta3) lib/action_view/rendering.rb:83:in `render_to_body' 
actionpack (5.0.0.beta3) lib/action_controller/metal/rendering.rb:52:in `render_to_body' 
actionpack (5.0.0.beta3) lib/action_controller/metal/renderers.rb:144:in `render_to_body' 
actionpack (5.0.0.beta3) lib/abstract_controller/rendering.rb:25:in `render' 
actionpack (5.0.0.beta3) lib/action_controller/metal/rendering.rb:36:in `render' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:43:in `block (2 levels) in render' 
activesupport (5.0.0.beta3) lib/active_support/core_ext/benchmark.rb:12:in `block in ms' 
/usr/local/Cellar/ruby/2.2.3/lib/ruby/2.2.0/benchmark.rb:303:in `realtime' 
activesupport (5.0.0.beta3) lib/active_support/core_ext/benchmark.rb:12:in `ms' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:43:in `block in render' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:86:in `cleanup_view_runtime' 
activerecord (5.0.0.beta3) lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:42:in `render' 
actionpack (5.0.0.beta3) lib/action_controller/metal/implicit_render.rb:19:in `default_render' 
actionpack (5.0.0.beta3) lib/action_controller/metal/basic_implicit_render.rb:4:in `block in send_action' 
actionpack (5.0.0.beta3) lib/action_controller/metal/basic_implicit_render.rb:4:in `tap' 
actionpack (5.0.0.beta3) lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action' 
actionpack (5.0.0.beta3) lib/abstract_controller/base.rb:183:in `process_action' 
actionpack (5.0.0.beta3) lib/action_controller/metal/rendering.rb:30:in `process_action' 
actionpack (5.0.0.beta3) lib/abstract_controller/callbacks.rb:20:in `block in process_action' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:126:in `call' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:126:in `call' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:506:in `block (2 levels) in compile' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:455:in `call' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:455:in `call' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:101:in `__run_callbacks__' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:750:in `_run_process_action_callbacks' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:90:in `run_callbacks' 
actionpack (5.0.0.beta3) lib/abstract_controller/callbacks.rb:19:in `process_action' 
actionpack (5.0.0.beta3) lib/action_controller/metal/rescue.rb:27:in `process_action' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action' 
activesupport (5.0.0.beta3) lib/active_support/notifications.rb:164:in `block in instrument' 
activesupport (5.0.0.beta3) lib/active_support/notifications/instrumenter.rb:21:in `instrument' 
activesupport (5.0.0.beta3) lib/active_support/notifications.rb:164:in `instrument' 
actionpack (5.0.0.beta3) lib/action_controller/metal/instrumentation.rb:29:in `process_action' 
actionpack (5.0.0.beta3) lib/action_controller/metal/params_wrapper.rb:248:in `process_action' 
activerecord (5.0.0.beta3) lib/active_record/railties/controller_runtime.rb:18:in `process_action' 
actionpack (5.0.0.beta3) lib/abstract_controller/base.rb:128:in `process' 
actionview (5.0.0.beta3) lib/action_view/rendering.rb:30:in `process' 
actionpack (5.0.0.beta3) lib/action_controller/metal.rb:190:in `dispatch' 
actionpack (5.0.0.beta3) lib/action_controller/metal.rb:262:in `dispatch' 
actionpack (5.0.0.beta3) lib/action_dispatch/routing/route_set.rb:50:in `dispatch' 
actionpack (5.0.0.beta3) lib/action_dispatch/routing/route_set.rb:32:in `serve' 
actionpack (5.0.0.beta3) lib/action_dispatch/journey/router.rb:39:in `block in serve' 
actionpack (5.0.0.beta3) lib/action_dispatch/journey/router.rb:26:in `each' 
actionpack (5.0.0.beta3) lib/action_dispatch/journey/router.rb:26:in `serve' 
actionpack (5.0.0.beta3) lib/action_dispatch/routing/route_set.rb:724:in `call' 
actionview (5.0.0.beta3) lib/action_view/digestor.rb:12:in `call' 
rack (2.0.0.alpha) lib/rack/etag.rb:25:in `call' 
rack (2.0.0.alpha) lib/rack/conditional_get.rb:25:in `call' 
rack (2.0.0.alpha) lib/rack/head.rb:12:in `call' 
rack (2.0.0.alpha) lib/rack/session/abstract/id.rb:220:in `context' 
rack (2.0.0.alpha) lib/rack/session/abstract/id.rb:214:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/cookies.rb:613:in `call' 
activerecord (5.0.0.beta3) lib/active_record/query_cache.rb:36:in `call' 
activerecord (5.0.0.beta3) lib/active_record/connection_adapters/abstract/connection_pool.rb:963:in `call' 
activerecord (5.0.0.beta3) lib/active_record/migration.rb:558:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:97:in `__run_callbacks__' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:750:in `_run_call_callbacks' 
activesupport (5.0.0.beta3) lib/active_support/callbacks.rb:90:in `run_callbacks' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/callbacks.rb:27:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/reloader.rb:71:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/remote_ip.rb:79:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/debug_exceptions.rb:49:in `call' 
web-console (3.1.1) lib/web_console/middleware.rb:131:in `call_app' 
web-console (3.1.1) lib/web_console/middleware.rb:28:in `block in call' 
web-console (3.1.1) lib/web_console/middleware.rb:18:in `catch' 
web-console (3.1.1) lib/web_console/middleware.rb:18:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call' 
railties (5.0.0.beta3) lib/rails/rack/logger.rb:36:in `call_app' 
railties (5.0.0.beta3) lib/rails/rack/logger.rb:24:in `block in call' 
activesupport (5.0.0.beta3) lib/active_support/tagged_logging.rb:70:in `block in tagged' 
activesupport (5.0.0.beta3) lib/active_support/tagged_logging.rb:26:in `tagged' 
activesupport (5.0.0.beta3) lib/active_support/tagged_logging.rb:70:in `tagged' 
railties (5.0.0.beta3) lib/rails/rack/logger.rb:24:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/request_id.rb:24:in `call' 
rack (2.0.0.alpha) lib/rack/method_override.rb:22:in `call' 
rack (2.0.0.alpha) lib/rack/runtime.rb:22:in `call' 
activesupport (5.0.0.beta3) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/load_interlock.rb:13:in `call' 
actionpack (5.0.0.beta3) lib/action_dispatch/middleware/static.rb:136:in `call' 
rack (2.0.0.alpha) lib/rack/sendfile.rb:111:in `call' 
railties (5.0.0.beta3) lib/rails/engine.rb:522:in `call' 
puma (3.4.0) lib/puma/configuration.rb:224:in `call' 
puma (3.4.0) lib/puma/server.rb:569:in `handle_request' 
puma (3.4.0) lib/puma/server.rb:406:in `process_client' 
puma (3.4.0) lib/puma/server.rb:271:in `block in run' 
puma (3.4.0) lib/puma/thread_pool.rb:114:in `call' 
puma (3.4.0) lib/puma/thread_pool.rb:114:in `block in spawn_thread' 

Answer 1

あなたはとてもコントローラで同じことをやって、ビュー層にpresentメソッドを呼び出すことで、プレゼンターとeventオブジェクトをラップするように見える私には冗長になります。さらに、それは実際にはwrong number of argumentsという結果の行でした。これは、単一の引数だけで囲みました。それを削除しましょう：

# events_controller 
def index 
    @events = Event.all 
    # we removed redundant EventPresenter.new(event) here 
end 

次のステップはあなたのビューテンプレートです。 @eventsに要素の配列が含まれている場合（presentヘルパーメソッドのpresentクラスのクラスを確認できます）、"ArrayPresenter".constantizeで終わる"#{object.class}Presenter".constantizeが返され、ArrayPresenterというクラスが存在しないため、エラーが発生します。あなたはこれが最初の配列を反復することで解決するために、ここで何ができるか：

<% @events.each do |event| %> 
    <% present event do |event_presenter| %> 

を別のオプションは、あなたのヘルパーメソッドの内部でコレクションを反復することができます。 Draper gemのようないくつかの既存のソリューションでは、オブジェクトのラッピング問題をどのように解決するかを知ることができます。