This is an industrial site where a pipe rack runs through several kilometres. This rack, as usual, has several bents, in this case, they call loops (even though they are not loops!) All the site is divided into areas. Each area can have several loops. Each loop can have several pipes. Not necessarily all the pipes that belong to an area pass through a loop.
My models are (simplified):
# models/loop.rb
class Loop < ActiveRecord::Base
belongs_to :area
has_many :pipes
end
# models/area.rb
class Area < ActiveRecord::Base
has_and_belongs_to_many :pipes
has_many :loops
has_many :looppipes, through: :loops, source: :pipes
end
# models/pipe.rb
class Pipe < ActiveRecord::Base
belongs_to :loop
has_and_belongs_to_many :areas
end
The line has_and_belongs_to_many :pipes gives the association for those pipes that have no loop associated.
To get the pipes that don’t pass through any loop of certain area, that is, pipes directly assigned, we can write
area.pipes
The line has_many :looppipes, through: :loops, source: :pipes in the area model gives the association area-pipe for those pipes that pass through a loop.
To get the pipes that go through any loop of certain area, we can write
area.looppipes
To join both lists we can write
area.pipes + area.looppipes
When the loop information is needed:
area.looppipes.includes(:loop)
area.looppipes.includes(:loop).first.loop.name
area.pipes.includes(:loop)
In the views
area/show.html.erb
<%= render partial: 'area_pipes', locals: { area: @area, pipes: @area.pipe, with_loop: false, listing_title: t(:Listing_pipes_without_loop) } unless @area.pipes.empty? %>
<%= render partial: 'area_pipes', locals: { area: @area, pipes: @area.looppipes.includes(:loop), with_loop: true, listing_title: t(:Listing_pipes_through_loop) } unless @area.looppipes.empty? %>
area/_area_pipes.html.erb
<h3><%= listing_title %></h3>
<table class="table table-striped">
<thead>
<tr>
<th><%= t :Name %></th>
<% if with_loop %> <th><%= t :Loop %></th> <% end -%>
<th class="centered"><%= t :Areas %></th>
<th colspan="1"></th>
</tr>
</thead>
<tbody>
<% pipes.each do |pipe| %>
<tr>
<td><%= pipe.name %></td>
<% if with_loop %> <td><%= pipe.loop.name %></td> <% end -%>
<td class="centered"><%= pipe.areas.count %></td>
<td><%= link_to t(:show_pipe_info), pipe if policy(Pipe).show? %></td>
<td><%= link_to t(:Remove_pipe), area_remove_pipe_path(area, pipe), method: :delete, data: { confirm: t(:Are_you_sure) } if policy(Area).remove_pipe? %></td>
</tr>
<% end %>
</tbody>
</table>