Change const_get to constantize to fix undefined method `default_scoped'

[joshua5201]

Found a strange problem when my namespace and model name are the same
(e.g. Order::Order)
config/routes

resources :order do
  resources :orders
end

When restart / modify source and the rails got reloaded, accessing /admin/order/orders and I get:

undefined method `default_scoped' for Order:Module

No problem if I get back to /admin and click the navigator link in the left.

And I found that in rails console

Object.const_get('Order::Order') 
=> Order
"Order::Order".constantize 
=> Order::Order

using constantize, I can get the correct model class name.

p.s. my model sources

app/models/order.rb

module Order
  def self.table_name_prefix
    'order_'
  end
end

app/models/order/order.rb

class Order::Order < ApplicationRecord
end

[joshua5201]

Don't know if the problem is related to rails' module and class loading. I tried in plain ruby with same class and module relationships, and there was no problem.

[pablobm]

So this is what I think is going on. I got to this conclusion after reading https://stackoverflow.com/questions/38086328/how-does-rubys-objectconst-get-actually-work

1. When you load the console, models are not loaded yet. Rails hasn't required them because it instead relies on autoloading.

2. Due to the way Object.const_get is implemented by Ruby, the call Object.const_get('Order::Order') is equivalent to Object.const_get('Order').const_get('Order').

3. When the first of these two const_get runs, Ruby gets to the point where a name is not defined, and Rails takes over, autoloading Order.

4. When the second const_get runs, it doesn't find an Order inside Order (it's not autoloaded yet). Before complaining about an undefined name, it goes up to the parent, Object, and asks again. There it finds an Order, which is the parent order. Autoloading of Order::Order never takes place.

ActiveSupport::Inflector#constantize uses a different algorithm. Internally it uses const_get, but it makes additional checks to avoid its weird behaviour. The documentation says:

The name is assumed to be the one of a top-level constant, no matter whether it starts with “::” or not.

This can sound confusing until you realise how const_get works internally.

@joshua5201's fix looks good to me, although my personal preference would be for using ActiveSupport::Inflector.constantize directly rather than an extension method. Eg:

ActiveSupport::Inflector.constantize(resource_class_name)

On the other hand, it's worth noting that Administrate doesn't support namespaced models at the moment. Other dangers may lay ahead.

[joshua5201]

@pablobm Thanks for your reply. I've changed to the implementation as you suggested
I think the current administrate support namespaced model in this pull request ?

[pablobm]

@joshua5201 I stand corrected, namespaces are supported now. Sorry!