我正在为nil：NilClass获取一个未定义的方法“ each”…但是它已定义？

Question

I've been searching for hours but I can't find the answer anywhere. I'm new to ruby on rails and I can't figure out how to fix this. What caused the problem is that I moved an instance variable from one file to another and now no links are working and the error always displays: undefined method `each' for nil:NilClass

here is my code:

Application.html.erb:

    <% number = 1 %>
      <% @projects.each do |project| %>
      <%= link_to project, id: "a-#{number}" do %>
      <div class="flex">
          <div class="each--project" id="project-<%= number %>">
              <h3><%= project.title %></h3>
              <p class="date"><%= project.created_at.strftime("%A, %b %d")%></p>
              <p class="content"><%= project.description %></p>
          </div>
      </div>
      <% number = number + 1 %>
      <% end %>
      <% end %>

application_controller.rb

    class ApplicationController < ActionController::Base
      def index
         @projects = Project.all
      end
      protect_from_forgery with: :exception
    end

projects_controller

        class ProjectsController < ApplicationController
          before_action :find_project, only: [:show, :edit, :update, :destroy]
          before_action :authenticate_user!, except: [:index, :show]
          def index
           @projects = Project.all.order("created_at desc")
          end

          def new
           @project = Project.new
          end

          def create
           @project = Project.new project_params

          if @project.save
           redirect_to @project, notice: "Yay Mia! That project was             saved!"
          else
             render 'new'
          end
         end

         def show
         end

         def edit
         end

         def update
           if @project.update project_params
             redirect_to @project, notice: "Yay Mia! That project was updated!"
           else
             render 'edit'
           end
         end

         def destroy
           @project.destroy
           redirect_to projects_path
         end


         private

         def find_project
           @project = Project.friendly.find(params[:id])
         end

         def project_params
           params.require(:project).permit(:title, :description, :link, :slug)
         end

       end

routes rb

   Rails.application.routes.draw do
     devise_for :users
     resources :posts
     resources :projects
     resources :contacts, only: [:new, :create]
     get 'welcome/index'
     root 'welcome#index'

     get '*path' => redirect('/')
   end

Answer 1

You don't have an index action on the ApplicationController You can however achieve the same thing with a before_action if you want it loaded for all actions in all controllers. This is not something I would recommend though.

class ApplicationController < ActionController::Base
  before_action :load_projects

  def load_projects
    @projects = Project.all
  end
end

Hint:

<% number = 1 %>
<% @projects.each do |project| %>

can be much better written as

<% @projects.each_with_index do |project, number| %>

Answer 2

If you're referencing something in your main application layout then it must be loaded for every controller. Putting it in one specific controller only engages it when that controller is in use, which it will only be on very specific routes.

If @projects needs to be populated on every request, move that to a load_projects method and add a before_action filter in your main ApplicationController. Putting it in a default index method doesn't work, that will never get run.

You can always stub in Rails.logger.debug('...') type calls to see if your code is actually being exercised. Watch log/development.log constantly to see what's happening. Most problems can be quickly resolved by examining what's been logged.