_debug_info

rake routes | grep group
           group_index GET    /group(.:format)                                  group#index
                       POST   /group(.:format)                                  group#create
             new_group GET    /group/new(.:format)                              group#new
            edit_group GET    /group/:id/edit(.:format)                         group#edit
                 group GET    /group/:id(.:format)                              group#show
                       PATCH  /group/:id(.:format)                              group#update
                       PUT    /group/:id(.:format)                              group#update
                       DELETE /group/:id(.:format)                              group#destroy
                       
2.0.0-p247 :003 > Group
 => Group(id: integer, name: string, created_at: datetime, updated_at: datetime)
 
Excerpt of routes.rb
...
  resources :device do
    resources :device_tags
  end
  resources :event do
    resources :event_tags
  end
  resources :group
  resources :production_state

  root 'event#index'
...

_form.html.erb

<%= form_for @group do |f| %>
  <% if @group.errors.any? %>
  <div id="error_explanation">
    <h2><%= pluralize(@group.errors.count, "error") %> prohibited
      this Group from being saved:</h2>
    <ul>
    <% @group.errors.full_messages.each do |msg| %>
      <li><%= msg %></li>
    <% end %>
    </ul>
  </div>
  <% end %>
  <p>
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </p>

  <p>
    <%= f.submit %>
  </p>
<% end %>
~

group_controller.rb

class GroupController < ApplicationController
  def index
    @groups = Group.all
    respond_to do |format|
      format.html { render html: @groups }
      format.json { render json: @groups.to_json }
    end
  end

  def new
    @group = Group.new
  end

  def show
    @group = Group.find(params[:id])
  end

  def edit
    @group = Group.find(params[:id])
  end
end

index.html.erb

<h1>Groups</h1>

<%= link_to 'New Group', new_group_path %>

<table>
    <thead>
    <tr>
        <th>Name</th>
    </tr>
    </thead>
    <tbody>
    <% @groups.each do |group| %>
    <tr>
        <td><%= link_to group.name edit_group_path(group) %></td>
    </tr>
    <% end %>
    </tbody
</table>
        

new.html.erb

<h1>New Group</h1>

<%= render 'form' %>

<%= link_to 'Back', group_index_path %>

rails_error.png

show.html.erb

<h1>Show Group</h1>

<%= link_to 'Back', group_index_path %>