Rails - routes - weird errors - ruby-on-rails

Question

I am making a rails 4 app.
I just created a scaffold for Universities.
The universities table has three attributes, being :name, :logo, :post_code.
I created three universities as a test. They come up in the console.
The university.rb model has these associations:
The university model has these associations:
has_many :faculties
has_many :students
has_many :academics#, through: :researchers
has_many :educators
has_many :faculties
has_many :courses, through: :faculties
has_many :programs#, through: :academics
has_many :alumnus
has_one :policy_ip
has_one :policy_publication
has_one :policy_commerciality
has_many :eaip_assets
has_many :commercial_ip_assets
has_many :community_activities
has_many :ip_transfer_successes
has_many :spin_outs
has_many :ip_asset_managers#, through: :universities
has_many :expression_of_interest_options#, through: :ip_asset_manager, -> { where submitted: true }
has_many :expression_of_interest_assignments#, through: :ip_asset_manager, -> { where submitted: true }
has_many :expression_of_interest_licensings#, through: :ip_asset_manager, -> { where submitted: true }
has_many :expression_of_interest_collaborations#, through: :ip_asset_manager, -> { where submitted: true }
has_many :expression_of_interest_spin_outs#, through: :ip_asset_manager, -> { where submitted: true }
has_many :awards
has_many :profiles
The view university#show has:
<div class="col-md-7 col-md-offset-1">
<div class="profilet"><%= #university.name %></div>
<%= link_to 'Edit', edit_university_path(#university) %> |
<%= link_to 'Back', universities_path %>
The first error I get (on each of my 3 records) is:
undefined method `name' for nil:NilClass
When I change the line so that it is on:
<div class="profilet"><%= #university.try(:name) %></div>
I get an error on the 'edit' link that says:
No route matches {:action=>"edit", :controller=>"universities", :id=>nil} missing required keys: [:id]
When I delete the edit link and try again, I get a blank page with a 'back' link.
I can't understand whats going wrong. My console shows I definitely have 3 records in the university table (each with an id 1, 2 or 3). My routes are resources - (as they are with all of my other models) and this is the first problem I've encountered with the edit link.
I have strong params in my universities controller for each of the three attributes in the table, so I"m stuck for things to try to do to fix this.
Any ideas?
The universities controller has:
class UniversitiesController < ApplicationController
# before_action :set_university, only: [:show, :edit, :update, :destroy]
# GET /universities
# GET /universities.json
def index
#universities = University.all
end
# GET /universities/1
# GET /universities/1.json
def show
end
# GET /universities/new
def new
#university = University.new
end
# GET /universities/1/edit
def edit
end
# POST /universities
# POST /universities.json
def create
#university = University.new(university_params)
respond_to do |format|
if #university.save
format.html { redirect_to #university, notice: 'University was successfully created.' }
format.json { render action: 'show', status: :created, location: #university }
else
format.html { render action: 'new' }
format.json { render json: #university.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /universities/1
# PATCH/PUT /universities/1.json
def update
respond_to do |format|
if #university.update(university_params)
format.html { redirect_to #university, notice: 'University was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #university.errors, status: :unprocessable_entity }
end
end
end
# DELETE /universities/1
# DELETE /universities/1.json
def destroy
#university.destroy
respond_to do |format|
format.html { redirect_to universities_url }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_university
#university = University.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def university_params
params[:university].permit(:name, :logo, :post_code)
end
end

Answer 1

It means you didn't have object university in the actions. You have to enable the line below:
before_action :set_university, only: [:show, :edit, :update, :destroy]

Answer 2

The associated instance variable #university is nil therefore the route helper could not generate a route for it.
Please check your controller's edit action and fix the problem there.

Answer 3

You have #university with the id=nil, if you want to use edit url helper you need to provide #university entity with the id. In other words you can edit record that exists in DB, otherwise you should create new.

Answer 4

Wow you have a lot of problems here.
undefined method `name' for nil:NilClass
This means one of your variables is not initialized. The cause of this is where the fun begins.
When you define <%= #university.x %>, you're calling a method on your #university variable. If that variable is not populated with any data, or is undefined, Ruby automatically assigns the NilClass class to it.
You mention you're seeing this error when referencing the #university variable. This means either in your routes or controller, it's not being populated.
Here's how to fix it:
#config/routes.rb
resources :universities #-> url.com/universities/:id
#app/controllers/universities_controller.rb
class UniversitiesController < ApplicationController
before_action :set_university, only: [:show, :edit, :update, :destroy]
def index
#universities = University.all
end
def edit
end
def show
end
end
This should give you the capacity to use the following:
#app/views/universities/show.html.erb
<% if #university %>
<%= #university.name %>
<% end %>