Trying to understand join tables in Rails

error.txt

NameError in LampsController#index
uninitialized constant Lamp::Constituents

Extracted source (around line #158):
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          end

          raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
        end
      end

index.html.erb

<p id="notice"><%= notice %></p>

<h1>Listing Lamps</h1>

<table class="table table-bordered table-condensed">
  <thead>
    <tr>
      <th>Model</th>
      <th>Description</th>
      <th>Sell</th>
      <th>Cost</th>
      <th>Stock</th>
      <th>Watt</th>
      <th>Width</th>
      <th>Length</th>
      <th>Fan</th>
      <th>LEDs/th>
      <th>PSU</th>
      <th>Led sum4</th>
      <th colspan="3"></th>
    </tr>
  </thead>

  <tbody>
    <% @lamps.each do |lamp| %>
      <tr>
        <td><%= lamp.model %></td>
        <td><%= lamp.description %></td>
        <td><%= lamp.sell %></td>
        <td><%= lamp.cost %></td>
        <td><%= lamp.stock %></td>
        <td><%= lamp.watt %></td>
        <td><%= lamp.width %></td>
        <td><%= lamp.length %></td>
        <td>
          <%= lamp.constituents.each do |c| %>
            <%= c.name %> | <%= c.count%>
          <% end %>
        </td>
        <td><%= lamp.led_sum2 %></td>
        <td><%= lamp.led_sum3 %></td>
        <td><%= lamp.led_sum4 %></td>
        <td><%= link_to 'Show', lamp %></td>
        <td><%= link_to 'Edit', edit_lamp_path(lamp) %></td>
        <td><%= link_to 'Destroy', lamp, method: :delete, data: { confirm: 'Are you sure?' } %></td>
      </tr>
    <% end %>
  </tbody>
</table>

<br>

<%= link_to 'New Lamp', new_lamp_path %>

joiner_schema

:lamp_id, :constituent_id, :sum

lamps_controller.rb

class LampsController < ApplicationController
  before_action :set_lamp, only: [:show, :edit, :update, :destroy]

  respond_to :html
 layout 'admin'
 
  def index
    @lamps = Lamp.all
  end

  def show
    respond_with(@lamp)
  end

  def new
    @lamp = Lamp.new
    respond_with(@lamp)
  end

  def edit
  end

  def create
    @lamp = Lamp.new(lamp_params)
    @lamp.save
    respond_with(@lamp)
  end

  def update
    @lamp.update(lamp_params)
    respond_with(@lamp)
  end

  def destroy
    @lamp.destroy
    respond_with(@lamp)
  end

  private
    def set_lamp
      @lamp = Lamp.find(params[:id])
    end

    def lamp_params
      params.require(:lamp).permit(:model, :description, :sell, :cost, :stock, :watt, :width, :length, :led_sum1, :led_sum2, :led_sum3, :led_sum4)
    end
end

models.rb

class Lamp < ActiveRecord::Base
  has_many :joiners
  has_many :constituents, through: :joiners
end

class Constituent < ActiveRecord::Base
  belongs_to :constituent_type
  has_many :joiners
  has_many :lamps, through: :joiners
end

class Joiner < ActiveRecord::Base
  belongs_to :constituents
  belongs_to :lamps
end