获取nil的未定义方法“+”：NilClass错误

时间：2013-06-22 01:29:13

标签： ruby-on-rails

我要做的是记录用户获得的睡眠量，然后能够根据月度范围以及年度范围显示每月睡眠中位数。 current_user是来自devise的一个帮助器，sleep = belongs_to user。用户has_many睡觉。

控制器：

def index
  @date = params[:date] ? Date.parse(params[:date]) : Date.today

  @sleeps = current_user.sleeps
  respond_to do |format|
    format.html { render action: 'index' }
    format.js
  end

  total_average_sleep_time = Array.new
  @sleeps.each do |average|
    average = average.hours
    total_average_sleep_time.push(average)
  end
  @total_average_sleep_time = median(total_average_sleep_time)

  month_range = current_user.sleeps.where(:sleep_date => @date.beginning_of_month..@date.end_of_month)
  monthly_average_sleep_time = Array.new
  month_range.each do |average|
    average = average.hours
    monthly_average_sleep_time.push(average)
  end
  @monthly_average_sleep_time = median(monthly_average_sleep_time)
end

private

def median(array)
  sorted = array.sort
  len = sorted.length
  return (sorted[(len - 1) / 2] + sorted[len / 2]) / 2.0
end

完整的错误消息：

Started GET "/sleeps" for 127.0.0.1 at 2013-06-21 18:34:50 -0700
Processing by SleepsController#index as HTML
  User Load (0.4ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 2 LIMIT 1
  Sleep Load (0.3ms)  SELECT "sleeps".* FROM "sleeps" WHERE "sleeps"."user_id" = 2
  Rendered sleeps/index.html.erb within layouts/application (17.1ms)
Completed 500 Internal Server Error in 115ms

NoMethodError (undefined method `+' for nil:NilClass):
app/controllers/sleeps_controller.rb:69:in `median'
app/controllers/sleeps_controller.rb:16:in `index'


Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.0ms)
Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (0.8ms)
Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (6.6ms)

完整追踪：

app/controllers/sleeps_controller.rb:69:in `median'
app/controllers/sleeps_controller.rb:16:in `index'
actionpack (3.2.13) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.13) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.13) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.13) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.13) lib/active_support/callbacks.rb:414:in `_run__271727191433844250__process_action__1430197560934326917__callbacks'
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.13) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.13) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.13) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.13) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.13) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.13) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.13) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.13) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.13) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.13) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.13) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.13) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.13) 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 (3.2.13) lib/action_dispatch/routing/route_set.rb:612:in `call'
omniauth (1.1.4) lib/omniauth/strategy.rb:184:in `call!'
omniauth (1.1.4) lib/omniauth/strategy.rb:164: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 (3.2.13) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.5) lib/rack/etag.rb:23:in `call'
rack (1.4.5) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context'
rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/cookies.rb:341:in `call'
activerecord (3.2.13) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.13) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `_run__3592650198556540672__call__1302268635398135570__callbacks'
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.13) lib/rails/rack/logger.rb:32:in `call_app'
railties (3.2.13) lib/rails/rack/logger.rb:16:in `block in call'
activesupport (3.2.13) lib/active_support/tagged_logging.rb:22:in `tagged'
railties (3.2.13) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.5) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.13) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.5) lib/rack/lock.rb:15:in `call'
actionpack (3.2.13) lib/action_dispatch/middleware/static.rb:63:in `call'
railties (3.2.13) lib/rails/engine.rb:479:in `call'
railties (3.2.13) lib/rails/application.rb:223:in `call'
rack (1.4.5) lib/rack/content_length.rb:14:in `call'
railties (3.2.13) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service'
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

任何人都可以向我解释为什么会这样吗？它在控制台中完美运行。是否有更清晰的方法来调试这样的问题？我知道这是由于中位数法的加法，但为什么呢？

1 个答案:

答案 0 :(得分：1)

median方法在空数组上爆炸，因为sorted[-1]不存在，因此尝试检索它会产生nil。

你可以加入一个保护条款，但是对于零数字的中位数没有明显的价值，imo。

另外，在一个样式笔记Enumerable#map上比#each和#push更好，再次imo。

愿Ruby与你同在。

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