<li><%= link_to "Company", company_path, :method => :get %></li>

No route matches {:action=>"show", :controller=>"companies"} missing required keys: [:id]

def current_company
  @company = Company.find_by_id(params[:id])
end

<%unless current_page?(root_path)||current_page?(companies_path)||current_company.nil? %>

   <li><%= link_to "Company", company_path, :method => :get %></li>

before_action :set_company, only: [:show, :edit, :update, :destroy, :company_home]

def company_home
  current_company = @company
  respond_with(@company)
end

def current_company=(company)
  session[:current_company] = company.id
  puts "The current_company has been assigned"
  puts params.inspect
end

def current_company
  @company = Company.find_by_id(session[:current_company])
  puts "The current_company helper has been called"
  puts @company
  puts params.inspect
end

def company_home
  puts "Test the current company"
  puts "#{@company.id} #{@company.name}"
  puts params.inspect
end

 private
  def set_company
    @company = Company.find_by_id(params[:id])
    if @company.nil?||current_user.organisation_id != @company.organisation.id
    flash[:alert] = "Stop poking around you nosey parker"
    redirect_to root_path
    else
    current_company = @company
    end
  end

Started GET "/company_home/1" for 80.55.210.105 at 2014-12-19 10:26:49 +0000
Processing by CompaniesController#company_home as HTML
  Parameters: {"authenticity_token"=>"gfdhjfgjhoFFHGHGFHJGhjkdgkhjgdjhHGLKJGJHpDQs6yNjONwSyTrdgjhgdjgjf=", "id"=>"1"}
  User Load (0.5ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = 6  ORDER BY "users"."id" ASC LIMIT 1
  Company Load (0.3ms)  SELECT  "companies".* FROM "companies"  WHERE "companies"."id" = 1 LIMIT 1
  Organisation Load (0.3ms)  SELECT  "organisations".* FROM "organisations"  WHERE "organisations"."id" = $1 LIMIT 1  [["id", 6]]
Test the current company
1 Cine
{"_method"=>"get", "authenticity_token"=>"gfdhjfgjhoFFHGHGFHJGhjkdgkhjgdjhHGLKJGJHpDQs6yNjONwSyTrdgjhgdjgjf=", "controller"=>"companies", "action"=>"company_home", "id"=>"1"}
  Rendered companies/company_home.html.erb within layouts/application (0.1ms)
  Company Load (0.6ms)  SELECT  "companies".* FROM "companies"  WHERE "companies"."id" IS NULL LIMIT 1
The current_company helper has been called

{"_method"=>"get", "authenticity_token"=>"gfdhjfgjhoFFHGHGFHJGhjkdgkhjgdjhHGLKJGJHpDQs6yNjONwSyTrdgjhgdjgjf=", "controller"=>"companies", "action"=>"company_home", "id"=>"1"}
  CACHE (0.0ms)  SELECT  "organisations".* FROM "organisations"  WHERE "organisations"."id" = $1 LIMIT 1  [["id", 6]]
Completed 200 OK in 280ms (Views: 274.0ms | ActiveRecord: 1.7ms)

def current_company=(company)
    session[:company_id]=company.id
end

def current_company
    Company.find_by_id(session[:company_id])
end

def show
    # assuming you have a before_action, something like set_company, no need to redo it
    current_company=@company # this will set the session variable
end

<% unless current_company.nil? %>
    <li><%= link_to "Company", current_company, :method => :get %></li>
<% end %>