gistfile1.rb

# Call ActiveRecord::base.forbid_implicit_checkout_for_thread! from a thread, and if
# that thread later tries to access an active record connection without explicit checkout
# (#with_connection, or #checkout), an ImplicitConnectionForbiddenError will be raised. 

module ActiveRecord
  class Base
    class << self
      def forbid_implicit_checkout_for_thread!
        Thread.current[:active_record_forbid_implicit_connections] = true
      end
      
      def connection
        if Thread.current[:active_record_forbid_implicit_connections] && ! thread_connected?
          raise ImplicitConnectionForbiddenError.new("Implicit ActiveRecord checkout attempted when Thread :force_explicit_connections set!")
        end
        retrieve_connection
      end
      
      # In Rails 3.1, this is connection_pool.active_connection? 
      # But we define our own so we have it in Rails 3.0 too. 
      def thread_connected?
        connection_id = connection_pool.send(:current_connection_id)
        connection_pool.instance_variable_get("@reserved_connections").has_key? connection_id
      end
      
    end           
  end  
  
  class ImplicitConnectionForbiddenError < ActiveRecord::ConnectionTimeoutError ; end
  
end

ActiveRecord::Base.forbid_implicit_checkout_for_thread!
ActiveRecord::Base.connection_pool.checkin(ActiveRecord::Base.connection_pool.connections.first)