調用Ruby類方法

Question

我已經建立了我Post模型中一個類的方法，像這樣：

def self.target_for_link 
    if @post.url == nil 
     puts "_blank" 
    else 
     puts "" 
    end 
end 

而且我從我的控制器調用它是這樣的：

@target = Post.target_for_link 

然而，我得到這個一No Method error (undefined method target_for_link)。我究竟做錯了什麼？

activerecord (5.1.3) lib/active_record/dynamic_matchers.rb:22:in `method_missing' 
app/controllers/posts_controller.rb:10:in `show' 
actionpack (5.1.3) lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action' 
actionpack (5.1.3) lib/abstract_controller/base.rb:186:in `process_action' 
actionpack (5.1.3) lib/action_controller/metal/rendering.rb:30:in `process_action' 
actionpack (5.1.3) lib/abstract_controller/callbacks.rb:20:in `block in process_action' 
activesupport (5.1.3) lib/active_support/callbacks.rb:131:in `run_callbacks' 
actionpack (5.1.3) lib/abstract_controller/callbacks.rb:19:in `process_action' 
actionpack (5.1.3) lib/action_controller/metal/rescue.rb:20:in `process_action' 
actionpack (5.1.3) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action' 
activesupport (5.1.3) lib/active_support/notifications.rb:166:in `block in instrument' 
activesupport (5.1.3) lib/active_support/notifications/instrumenter.rb:21:in `instrument' 
activesupport (5.1.3) lib/active_support/notifications.rb:166:in `instrument' 
actionpack (5.1.3) lib/action_controller/metal/instrumentation.rb:30:in `process_action' 
actionpack (5.1.3) lib/action_controller/metal/params_wrapper.rb:252:in `process_action' 
activerecord (5.1.3) lib/active_record/railties/controller_runtime.rb:22:in `process_action' 
actionpack (5.1.3) lib/abstract_controller/base.rb:124:in `process' 
actionview (5.1.3) lib/action_view/rendering.rb:30:in `process' 
actionpack (5.1.3) lib/action_controller/metal.rb:189:in `dispatch' 
actionpack (5.1.3) lib/action_controller/metal.rb:253:in `dispatch' 
actionpack (5.1.3) lib/action_dispatch/routing/route_set.rb:49:in `dispatch' 
actionpack (5.1.3) lib/action_dispatch/routing/route_set.rb:31:in `serve' 
actionpack (5.1.3) lib/action_dispatch/journey/router.rb:46:in `block in serve' 
actionpack (5.1.3) lib/action_dispatch/journey/router.rb:33:in `each' 
actionpack (5.1.3) lib/action_dispatch/journey/router.rb:33:in `serve' 
actionpack (5.1.3) lib/action_dispatch/routing/route_set.rb:834:in `call' 
warden (1.2.7) lib/warden/manager.rb:36:in `block in call' 
warden (1.2.7) lib/warden/manager.rb:35:in `catch' 
warden (1.2.7) lib/warden/manager.rb:35:in `call' 
rack (2.0.3) lib/rack/etag.rb:25:in `call' 
rack (2.0.3) lib/rack/conditional_get.rb:25:in `call' 
rack (2.0.3) lib/rack/head.rb:12:in `call' 
rack (2.0.3) lib/rack/session/abstract/id.rb:232:in `context' 
rack (2.0.3) lib/rack/session/abstract/id.rb:226:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/cookies.rb:613:in `call' 
activerecord (5.1.3) lib/active_record/migration.rb:556:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/callbacks.rb:26:in `block in call' 
activesupport (5.1.3) lib/active_support/callbacks.rb:97:in `run_callbacks' 
actionpack (5.1.3) lib/action_dispatch/middleware/callbacks.rb:24:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/executor.rb:12:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/debug_exceptions.rb:59:in `call' 
web-console (3.5.1) lib/web_console/middleware.rb:135:in `call_app' 
web-console (3.5.1) lib/web_console/middleware.rb:28:in `block in call' 
web-console (3.5.1) lib/web_console/middleware.rb:18:in `catch' 
web-console (3.5.1) lib/web_console/middleware.rb:18:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call' 
railties (5.1.3) lib/rails/rack/logger.rb:36:in `call_app' 
railties (5.1.3) lib/rails/rack/logger.rb:24:in `block in call' 
activesupport (5.1.3) lib/active_support/tagged_logging.rb:69:in `block in tagged' 
activesupport (5.1.3) lib/active_support/tagged_logging.rb:26:in `tagged' 
activesupport (5.1.3) lib/active_support/tagged_logging.rb:69:in `tagged' 
railties (5.1.3) lib/rails/rack/logger.rb:24:in `call' 
sprockets-rails (3.2.0) lib/sprockets/rails/quiet_assets.rb:13:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/remote_ip.rb:79:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/request_id.rb:25:in `call' 
rack (2.0.3) lib/rack/method_override.rb:22:in `call' 
rack (2.0.3) lib/rack/runtime.rb:22:in `call' 
activesupport (5.1.3) lib/active_support/cache/strategy/local_cache_middleware.rb:27:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/executor.rb:12:in `call' 
actionpack (5.1.3) lib/action_dispatch/middleware/static.rb:125:in `call' 
rack (2.0.3) lib/rack/sendfile.rb:111:in `call' 
railties (5.1.3) lib/rails/engine.rb:522:in `call' 
puma (3.10.0) lib/puma/configuration.rb:225:in `call' 
puma (3.10.0) lib/puma/server.rb:605:in `handle_request' 
puma (3.10.0) lib/puma/server.rb:437:in `process_client' 
puma (3.10.0) lib/puma/server.rb:301:in `block in run' 
puma (3.10.0) lib/puma/thread_pool.rb:120:in `block in spawn_thread' 

Answer 1

我不能說，爲什麼你有這種特殊的錯誤，但你的方法是怪異。你瞭解類和實例方法之間的差異嗎？

這是一個類的方法，但你使用@port屬性猶如狀態要緊。你不想做這樣的事情

def target_for_link 
    if self.url == nil # you could actually ommit `self.` part here 
     puts "_blank" 
    else 
     puts "" 
    end 
end 

，然後在控制器

@post = Post.find(1) 
@target = @post.target_for_link 

還有一兩件事：爲什麼要使用看跌期權呢？我無法猜測。但我認爲你想返回值「_blank」或「」視後url和你做這樣的：

def target_for_link 
    if url == nil 
     "_blank" 
    else 
     "" 
    end 
end 

否則你會被返回調用puts方法是nil的結果。