rails: ActiveSupport::Cache::Store(s) fails to autoload classes

Environment:

1. Ruby 1.9.3-p327 (happens also in p0)
2. Rails 3.2.8 (happens also in 3.2.3)

Steps to reproduce:

1. create a new project using: rails new autoload_bug
2. create some model: rails g model user
3. rails c and then type this code:

Rails.cache.write("test",User)

1. close that irb, rails c and type:

Rails.cache.read("test")

Expected:

This should work like any other code that depends on Rails autoloading.

Actual:

It fails with the following error:

ArgumentError: undefined class/module User
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.8/lib/active_support/cache.rb:587:in `load'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.8/lib/active_support/cache.rb:587:in `value'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.8/lib/active_support/cache.rb:324:in `block in read'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.8/lib/active_support/cache.rb:520:in `instrument'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.8/lib/active_support/cache.rb:315:in `read'
    from (irb):1
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.8/lib/rails/commands/console.rb:47:in `start'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.8/lib/rails/commands/console.rb:8:in `start'
    from /home/uriel/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.8/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

Why this is important?

This is important in development (in production config.cache_classes = true takes care of this) because if I just start my rails server and the first requests fetches some instance that the class wasn’t already loaded (typical case the User object) it will crash.

I have seen other people ran into this problem and their conclusion was either enable config.cache_classes (yuck) or loading all the models at app start.

Note: I used the class and not an instance as creating an instance requires creating a database table and I wanted to keep it simple. It happens with instances too.

The source of this bug:

All stores (from what I checked) works with Marshal#load and it seems the autoloading mechanism in rails doesn’t work for Marshal#load (I guess because it is native code)

Related links:

Other people that had this bug: http://www.philsergi.com/2007/06/rails-memcached-undefinded-classmodule.html http://stackoverflow.com/questions/4202352/memcached-problem-with-rails-3-object-isnt-being-deserialized-the-second-time http://blog.endpoint.com/2012/08/rails-3-activerecord-caching-bug-ahoy.html

Possible solution: http://stackoverflow.com/questions/3531588/memcached-as-an-object-store-in-rails