Rails core - Nov 2007 - purpose of ActiveRecord::Base.reset_subclasses?

ActionController::Dispatcher#cleanup_application does this:

    def cleanup_application(force = false)
      if Dependencies.load? || force
        ActiveRecord::Base.reset_subclasses if defined?(ActiveRecord)
        Dependencies.clear
        ActiveRecord::Base.clear_reloadable_connections! if
defined?(ActiveRecord)
      end
    end

where

    def self.reset_subclasses #:nodoc:
      nonreloadables = []
      subclasses.each do |klass|
        unless Dependencies.autoloaded? klass
          nonreloadables << klass
          next
        end
        klass.instance_variables.each { |var|
klass.send(:remove_instance_variable, var) }
        klass.instance_methods(false).each { |m| klass.send :undef_method, m }
      end
      @@subclasses = {}
      nonreloadables.each { |klass| (@@subclasses[klass.superclass]
||= []) << klass }
    end

Why do ARs need that cleanup?

-- fxn

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On E, 2007-11-19 at 11:26 +0100, Xavier Noria wrote:
> Why do ARs need that cleanup?
Probably because they have to reload the database schema
which is partly described in their class instance variables
on every request.

For example, columns:

      # Returns an array of column objects for the table associated with
this class.
      def columns
        unless @columns
          @columns = connection.columns(table_name, "#{name} Columns")
          @columns.each {|column| column.primary = column.name =primary_key}
        end
        @columns
      end

-- 
Tarmo Tänav <tarmo@itech.ee>


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On Nov 19, 12:16 pm, Tarmo Tänav <ta...@itech.ee> wrote:
> On E, 2007-11-19 at 11:26 +0100, Xavier Noria wrote:
>
> > Why do ARs need that cleanup?
>
> Probably because they have to reload the database schema
> which is partly described in their class instance variables
> on every request.
But if the class was autoloaded wouldn''t that be a side-effect of
remove_const Model + const_missing Model as with the rest of
autoloaded classes? Why are those special removals needed?

-- fxn


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> But if the class was autoloaded wouldn''t that be a side-effect of
> remove_const Model + const_missing Model as with the rest of
> autoloaded classes? Why are those special removals needed?
Indeed that does seem unneeded at first glance.  Another thing to test
out once 2.0 is out the door I guess ;)

-- 
Cheers

Koz

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