Having trouble adding view created from a has_many: through table. - ruby-on-rails

Question

Hopefully I get all the terminology right here - if not please forgive, still very new.
I am working on a course project #Bloc and am having trouble with adding a list of collaborators to my index view for a different controller.
What I am trying to achieve is:
Show all user wikis - working.
Show all wikis where user is listed as a collaborator (link created through a join table and has_many through reference.)
My index view looks like: (/wikis/index)
<h1>My Wikis</h1>
<% if policy(Wiki.new).create? %>
<%= link_to "New Wiki", new_wiki_path, class: 'btn btn-success' %>
<% end %>
<% #wikis.each do |wikis| %>
<div class="media">
<div class="media-body">
<h4 class="media-heading">
<%= link_to wikis.title, wikis %>
</h4>
<small>
Created <%= time_ago_in_words(wikis.created_at) %> ago by <%= wikis.user.name %><br/>
</small>
</div>
</div>
<% end %>
<h1>My Collaborations</h1>
<% #collaborations.each do |collaborations| %>
<div class="media">
<div class="media-body">
<h4 class="media-heading">
<%= link_to collaborations.title, collaborations %>
</h4>
</div>
</div>
<% end %>
<%= will_paginate #wikis %>
My Wikis controller looks like: (shortened)
class WikisController < ApplicationController
respond_to :html, :js
def index
# #user = current_user
#wikis = current_user.wikis.paginate(page: params[:page], per_page: 10)
##collaboration = #wiki.collaboration.build(collaboration_params)
#collaborations = #collaboration.where(:user_id == current_user)
authorize #wikis
end
def show
#wikis = Wiki.friendly.find(params[:id])
if request.path != wiki_path(#wikis)
redirect_to #wikis, status: :moved_permanently
authorize #wikis
end
end
end
private
def collaboration_params
params.require(:collaboration).permit(:user_id, :wiki_id)
end
end
From the Rails Console - I can see that my collaboration relationship is working as expected - I just cannot quite figure out what the syntax is I should be using to make it render on my index view.
2.0.0-p481 :022 > Collaboration.last
Collaboration Load (1.9ms) SELECT "collaborations".* FROM "collaborations" ORDER BY "collaborations"."id" DESC LIMIT 1
log writing failed. Protocol error - /home/vagrant/code/blocipedia/log/development.log
=> #<Collaboration id: 3, user_id: 1, wiki_id: 16>
2.0.0-p481 :023 >
Any pointers would be greatly appreciated. I've tried what feels like about 100 different combinations to figure this out.
Right now the error I trigger on index view is:
undefined method `where' for nil:NilClass
Cheers
Kevin.

Answer 1

Object
The simple error you have is here:
#collaborations = #collaboration.where(:user_id == current_user)
The error here is that you're calling .where on a variable which has not been populated (defined).
Ruby / Rails works somewhat differently to other languages, in that it's object orientated. This means that each time Rails calls an "object", it will actually be defined, just not populated.
As a rule of thumb, the no method error is generally (although not always) a result of the system having not populated the variable correctly.
Model
The way to fix this is very simple -
You just need to be able to declare the #collaboration object before calling the .where method: on it. However, as you're using the .build method to define this object, you're not going to get anywhere.
Essentially, when you perform a .where lookup, you'll be using ActiveRecord to ping the datatables in the backend, populating an object with the various attributes from the Model (look up MVC programming pattern for more about this)
What you need to do (if you want to call .where) is create an instance of the model you wish to query inside the database. To do this, you either have to call the model directly, or through an associative object:
def index
#wikis = current_user.wikis.paginate(page: params[:page], per_page: 10)
#collaborations = Collaboration.where(user_id: current_user.id)
authorize #wikis
end
System
As you're new to Rails, let me give you some details on how to make the system work properly.
Firstly, you need to appreciate the role of ActiveRecord Associations - these are built on the ActiveRecord pattern, making it much simpler to build "objects" around database-driven data
In short, if you associate two or more objects with ActiveRecord, it means you can call the associative data through the primary object:
#app/models/user.rb
Class User < ActiveRecord::Base
has_many :collaborations
end
#app/models/collaboration.rb
Class Collaboration < ActiveRecord::Base
belongs_to :user
end
This means that instead of calling #collaborations = Collaboration.where(user_id: current_user.id), you'll simply be able to call#collaborations = current_user.collaborations`
Fix
The fix should be as follows:
#app/views/wiki/index.html.erb
...
<% current_user.collaborations.each do |collaboration| %>
<div class="media">
<div class="media-body">
<h4 class="media-heading">
<%= link_to collaboration.title, collaboration %>
</h4>
</div>
</div>
<% end %>
#app/controllers/wikis_controller.rb
Class WikisController < ApplicationController
def index
#wikis = current_user.wikis.paginate(page: params[:page], per_page: 10)
authorize #wikis
end
end