Rendering partial that belongs to another controller - ruby

Question

I've got a menu controller, which is set as my root controller in routes.rb. In my menu view, i try and render the _lights.slim partial with = render :partial => 'lights/lights' but i get the following error: undefined method `lights' for nil:NilClass
MenuController:
class MenuController < ApplicationController
def index
end
end
Menu View (index.slim)
ul.tabs.vertical data-tab=""
li.tab-title.active
a href="#panel1a" Tab 1
.tabs-content.vertical
#panel1a.content.active
= render :partial => 'lights/lights'
LightsController
class LightsController < ApplicationController
before_action :discover_lights
include LIFX
#client = LIFX::Client.lan
#client.discover!
3.times do
#client.lights.refresh
sleep (0.5)
puts "Found #{#client.lights.count} with labels #{#client.lights}"
end
def index
end
def new
end
def light_toggle
light = #client.lights.with_label(params[:label])
light.on? ? light.turn_off : light.turn_on
redirect_to '/'
end
private
def discover_lights
#client = LIFX::Client.lan
#client.discover!
end
end
Lights View (_lights.slim)
h1.subheader LIFX Lights
table.light-table
thead
tr
th Light
th Status
th Power On/Off
th Brightness
tbody
-#client.lights.map do |c|
tr
th #{c.label}
th #{c.power}
th =link_to 'Toggle', light_path(:label => c.label)
th #{c.color.brightness.round(2) * 100}%
end
Routes.rb
root 'menu#index'
get '/lights', to: 'lights#index'
get '/lights/:label', to: 'lights#light_toggle', as: 'light'
I know this is a no brainer, but i'm stuck as to what to do here. I'm thinking it must be an issue with the way that when Menu#Index is called, I never knows about my LightsController, and so #client.blablabla will never make sense. But how will I make my app know about my LightsController when the view is loaded as a partial

Answer 1

Partials
You must appreciate that Partials are not controller-dependent (being stored in a controllers' view directory does not tie them for use with that controller)
This means if you have the functionality to support the partial in another controller, you should be able to use it in different parts of your app
--
Error
This leads us to the identification of the problem you're receiving.
It's not the calling of the partial which causes an issue - it's how you're referring to the code inside it:
undefined method `lights' for nil:NilClass
The error is clearly that you're trying to call the lights method on an object / variable which doesn't exist. This is defined inside the partial itself here:
#client.lights.map do |c|
Therefore, you need to be able to pass the correct data to the partial, enabling it to load the #client object without being dependent on the controller
--
Fix
To do this, you may wish to consider using partial locals -
<%= render partial: "lights/lights", locals: {client: #client} %>
This means that every time you call the partial, you'll have to pass the #client object into the client local var, thus allowing the partial to run controller-independently.
Here's how you'd handle it in the partial itself:
#app/views/lights/_lights.slim
- client.lights.map do |c|