Rails - Jan 2005 - Storing temporary defaults in the session under the controller''s namespace

I made a handy feature for those who need persistent "settings" or
defaults at the session level--this snippet of code was useful to me
when I had a list view that had options such as "sort by" and
"show
only this category".  When the user re-visits the list view after
having visited an arbitrary number of other pages, I wanted the view
to stay the way the user had it when they left it.  As a result, the
following code separates these little "defaults" in the session in to
controller namespaces and stores the values in the session.

For example:
store_default :category_id, @params[''category_id''].to_i

results in

@session[''MerchandiseController''][''category_id'']
= @params[''category_id''].to_i

which is later automagically retrieved by load_defaults as
@category_id in the MerchandiseController class.

Duane

CODE SNIPPETS:

Usage:
  in MerchandiseController I have the following:

class MerchandiseController < ApplicationController
  before_filter :load_defaults
 
  def list
    # First thing, load any saved defaults, or set them if called to do so
    # (If the user hits the ''reload'' button, defaults are
saved.)
    if (@params[''reload''])
      store_default :category_id, @params[''category_id''].to_i
      store_default :order_by, @params[''order_by'']
    end
    ...
  end

end 


And in application.rb:
 
 
  # Given a symbol (key), store the value in both an instance
  # variable AND the session so that it can be loaded again at
  # some arbitrary time later on (for example, when the user
  # re-visits a certain page, and you want the same information
  # to be displayed).
  # Example (assuming the call is made from MerchandiseController):
  # store_default :order_by, "name"
  #   => "name"
  #   (side effect: store "name" in @order_by and
  #   
@session[''MerchandiseController''][''order_by''])
  def store_default(key, value)
    className = self.class.to_s
    keyName = key.id2name
 
    # Make sure there''s a namespace for this class''s defaults
    @session[className] ||= Hash.new
 
    # Store the key/value in the session
    @session[className][keyName] = value
 
    # Store the key/value as an instance variable
    if (value.is_a? String)
      eval "@#{keyName} = ''#{value}''"
    else
      eval "@#{keyName} = #{value}"
    end
  end
 
  # Given a symbol, load its string-equivalent from the session
  # and store it in an instance variable.  For example, if the
  # method is called from within the class "MerchandiseController"
  # as "load_default :category_id" then this method will retrieve
  #
@session[''MerchandiseController''][''category_id'']
and store it
  # in @category_id.
  def load_default(key)
    begin
      value = @session[self.class.to_s][key.id2name]
      if (value.is_a? String)
        eval "@#{key.id2name} = ''#{value}''"
      else
        eval "@#{key.id2name} = #{value}"
      end
    rescue
      nil
    end
  end
 
  # Load all of the values stored in the session (only the
  # ones stored for this class) and create instance variables
  # for each.  So for example, if
@session[''MerchandiseController'']
  # contains the Hash { ''category_id'' => 1,
''order_by'' => ''name'' },
  # then load_defaults will make @category_id = 1 and
  # @order_by = ''name''.
  def load_defaults
        return if @session[self.class.to_s] == nil
 
    @session[self.class.to_s].each do |key,value|
      if (value.is_a? String)
        eval "@#{key} = ''#{value}''"
      else
        eval "@#{key} = #{value}"
      end
    end
  end