No route matches {:action=>"show" ... missing required keys: [:id] - ruby-on-rails-4

Question

Seeing many question related to this but none of them gives answer to my problem.
I have Rails api application without ActiveRecord support. It is easy to reproduce problem. Follow steps:
Create rails api site without ActiveRecord support
rails new test001 -O --api
Change folder to test001 and run:
rails g scaffold testapp id name
Create model file testapp.rb in app/models folder
class Testapp
include ActiveModel::Model
attr_accessor :id, :name, :created_at, :updated_at
def self.all
t1 = Testapp.new(:id =>111, name: "t111")
return [t1]
end
end
Start server
rails s
Using postman REST client create GET request
http://localhost:3000/testapps.json
It fails with error ActionView::Template::Error (No route matches {:action=>"show", :controller=>"testapps", :format=>:json, :id=>#<Testapp:0x00000005411518 #id=111, #name="t111">} missing required keys: [:id]):
I have dummy implementation for POST, PUT, GET 1 item and all works. Here is dummy implementation of GET 1 item (/testapps/x.json)
def self.find(p)
return Testapp.new(:id =>p, name: "t123")
end
What is the problem with GET all (/testapps.json)?

Answer 1

Found solution.
Problem is scaffold generated index.json.jbuilder
file:
json.array!(#testapps) do |testapp|
json.extract! testapp, :id, :id, :name
json.url testapp_url(testapp, format: :json) #REMOVE
end
It added line json.url testapp_url(testapp, format: :json) for no reason. json.extract! deserialized object already.
Removing line solved problem.
I still do not know why testapp_url(testapp, format:json) caused error. Checking Rails Routing document http://guides.rubyonrails.org/routing.html