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Greg Hauptmann

2006-Sep-04 07:34 UTC

what is "cattr_accessor" (used in acts_as_audited)

Hi,

Just trying to understand what "cattr_accessor" is in the 
acts_as_audited plugin.  Any ideas?

[In particular I''m trying to understand how to create the appropriate 
User class so I can turn on logging of userid - I''m using activeRBAC
for
authentication]

Example usage:

cattr_accessor :non_audited_columns, :audited_user_class_name, 
:audited_user_method


Full extract from plugin (used within here):
=================================================# Copyright (c) 2006 Brandon
Keepers
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

module CollectiveIdea #:nodoc:
  module Acts #:nodoc:
    # Specify this act if you want changes to your model to be saved in 
an
    # audit table.  This assumes there is an audits table ready.
    #
    #   class User < ActiveRecord::Base
    #     acts_as_audited
    #   end
    #
    # See 
<tt>CollectiveIdea::Acts::Audited::ClassMethods#acts_as_audited</tt>
    # for configuration options
    module Audited
      CALLBACKS = [:clear_changed_attributes, :audit_create, 
:audit_update, :audit_destroy]

      def self.included(base) # :nodoc:
        base.extend ClassMethods
      end

      module ClassMethods
        # == Configuration options
        #
        # * <tt>except</tt> - Excludes fields from being saved in
the
audit log.
        #   By default, acts_as_audited will audit all but these fields:
        #
        #     [self.primary_key, inheritance_column,
''lock_version'',
''created_at'', ''updated_at'']
        #
        #   You can add to those by passing one or an array of fields to 
skip.
        #
        #     class User < ActiveRecord::Base
        #       acts_as_audited :except => :password
        #     end
        #
        # * <tt>user_class_name</tt> - specifiy the class name of
the
user class.
        #   This defaults to "User". Set to false to disable user 
auditing.
        #
        # * <tt>user_method</tt> - specify the method to call on 
<tt>:user_class_name</tt>
        #   that returns the user that is performing the action. This 
defaults to
        #   <tt>:current_user</tt>.
        #
        # == Database Schema
        #
        def acts_as_audited(options = {})
          # don''t allow multiple calls
          return if 
self.included_modules.include?(CollectiveIdea::Acts::Audited::InstanceMethods)

          include CollectiveIdea::Acts::Audited::InstanceMethods

          class_eval do
            extend CollectiveIdea::Acts::Audited::SingletonMethods

            cattr_accessor :non_audited_columns, 
:audited_user_class_name, :audited_user_method

            self.non_audited_columns = [self.primary_key, 
inheritance_column, ''lock_version'',
''created_at'', ''updated_at'']
            self.non_audited_columns |= options[:except].is_a?(Array) ?
              options[:except].collect{|column| column.to_s} : 
[options[:except].to_s] if options[:except]
            self.audited_user_class_name = 
options[:user_class_name].nil? ? "User" : options[:user_class_name]
            self.audited_user_method = options[:user_method] || 
:current_user

            has_many :audits, :as => :auditable
            after_create :audit_create
            after_update :audit_update
            before_destroy :audit_destroy
            after_save :clear_changed_attributes
          end
        end
      end

      module InstanceMethods
        # Temporarily turns off auditing while saving.
        def save_without_auditing
          without_auditing do
            save
          end
        end

        # Returns an array of attribute keys that are audited.  See 
non_audited_columns
        def audited_attributes
          self.attributes.keys.select { |k| 
!self.class.non_audited_columns.include?(k) }
        end

        # If called with no parameters, gets whether the current model 
has changed.
        # If called with a single parameter, gets whether the parameter 
has changed.
        def changed?(attr_name = nil)
          attr_name.nil? ?
            (@changed_attributes && @changed_attributes.length > 0) :
            (@changed_attributes && 
@changed_attributes.include?(attr_name.to_s))
        end

        # Executes the block with the auditing callbacks disabled.
        #
        #   @foo.without_auditing do
        #     @foo.save
        #   end
        #
        def without_auditing(&block)
          self.class.without_auditing(&block)
        end

        private
          # Creates a new record in the audits table if applicable
          def audit_create
			logger.debug "ACTS AS: audit_create"
            write_audit(:create)
          end

          def audit_update
            write_audit(:update) if changed?
          end

          def audit_destroy
            write_audit(:destroy)
          end

          def write_audit(action = :update)
			logger.debug "ACTS AS: write_audit"
		    logger.debug "ACTS AS: self.audited_user_class_name = 
#{self.audited_user_class_name}"
			#logger.debug "ACTS AS: Object.const_get(audited_user_class_name) = 
#{Object.const_get(audited_user_class_name)}"
			logger.debug "ACTS AS: self.audited_user_method = 
#{self.audited_user_method}"
            user = self.audited_user_class_name ? 
Object.const_get(audited_user_class_name).send(self.audited_user_method) 
: nil

            logger.debug "ACTS AS: user = #{user}"
			audits.create(:changes => @changed_attributes, :action => 
action.to_s,
              :user_id => user ? user.id : nil)
          end

          # clears current changed attributes.  Called after save.
          def clear_changed_attributes
            @changed_attributes = {}
          end

          # overload write_attribute to save changes to audited 
attributes
          def write_attribute(attr_name, attr_value)
            attr_name = attr_name.to_s
            if audited_attributes.include?(attr_name)
              @changed_attributes ||= {}
              # get original value
              old_value = @changed_attributes[attr_name] ?
                @changed_attributes[attr_name].first : self[attr_name]
              super(attr_name, attr_value)
              new_value = self[attr_name]

              @changed_attributes[attr_name] = [old_value, new_value] if 
new_value != old_value
            else
              super(attr_name, attr_value)
            end
          end

          CALLBACKS.each do |attr_name|
            alias_method "orig_#{attr_name}".to_sym, attr_name
          end

          def empty_callback() end #:nodoc:

      end # InstanceMethods

      module SingletonMethods
        # Returns an array of columns that are audited.  See 
non_audited_columns
        def audited_columns
          self.columns.select { |c| 
!non_audited_columns.include?(c.name) }
        end

        # Executes the block with the auditing callbacks disabled.
        #
        #   Foo.without_auditing do
        #     @foo.save
        #   end
        #
        def without_auditing(&block)
          class_eval do
            CALLBACKS.each do |attr_name|
              alias_method attr_name, :empty_callback
            end
          end
          result = block.call
          class_eval do
            CALLBACKS.each do |attr_name|
              alias_method attr_name, "orig_#{attr_name}".to_sym
            end
          end
          result
        end
      end
    end
  end
end

ActiveRecord::Base.send :include, CollectiveIdea::Acts::Audited

=================================================
-- 
Posted via http://www.ruby-forum.com/.

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Zachary Holt

2006-Sep-04 08:52 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

Hi Greg,

On Sep 4, 2006, at 12:34 AM, Greg Hauptmann wrote:
> Just trying to understand what "cattr_accessor" is in the
> acts_as_audited plugin.  Any ideas?
Check out

activesupport/lib/active_support/core_ext/class/attribute_accessors.rb

You can think of cattr_accessor as an attr_accessor for a class (thus  
the ''c''), instead of for an instance of a class.  Essentially,
it''s a
little sugar to make life easier when giving classes read/write  
attributes.  (Not that such things are difficult in Ruby proper.)


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Greg H

2006-Sep-04 10:35 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

Had a quick look at this (e.g. cattr_reader - extract below) - still I
little unclear to me.  Do you think you could run what
"cattr_accessor" does
in layman''s terms at all?  e.g. difference between class & instant
aspects.   (sorry - the penny hasn''t dropped yet :)  )

================  def cattr_reader(*syms)
    syms.flatten.each do |sym|
      class_eval(<<-EOS, __FILE__, __LINE__)
        unless defined? @@#{sym}
          @@#{sym} = nil
        end

        def self.#{sym}
          @@#{sym}
        end

        def #{sym}
          @@#{sym}
        end
      EOS
    end
  end
====================

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Ian Leitch

2006-Sep-04 11:14 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

class Songs

    @@play_count = 0

    def  self.play_count
        # The cattr_reader thang
         @@play_count
    end

    def play
        @@play_count += 1
    end

end

song1 = Songs.new
song1.play> 1song2 = Songs.new
song2.play> 2
Songs.play_count> 2

Hope that helps.


On 04/09/06, Greg H
<greg.hauptmann.ruby-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> Had a quick look at this (e.g. cattr_reader - extract below) - still I
> little unclear to me.  Do you think you could run what
"cattr_accessor" does
> in layman''s terms at all?  e.g. difference between class &
instant
> aspects.   (sorry - the penny hasn''t dropped yet :)  )
>
> ================>   def cattr_reader(*syms)
>     syms.flatten.each do |sym|
>       class_eval(<<-EOS, __FILE__, __LINE__)
>         unless defined? @@#{sym}
>           @@#{sym} = nil
>         end
>
>         def self.#{sym}
>           @@#{sym}
>         end
>
>         def #{sym}
>           @@#{sym}
>         end
>       EOS
>     end
>   end
> ====================>
>
> >
>

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Greg H

2006-Sep-04 11:21 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

thanks Ian - I think I got it - just have to go back and make sense of this
within the code that was also doing multiple modules / includes / and
extends  :)


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dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Sep-04 11:39 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

Hi --

On Mon, 4 Sep 2006, Greg H wrote:
> Had a quick look at this (e.g. cattr_reader - extract below) - still I
> little unclear to me.  Do you think you could run what
"cattr_accessor" does
> in layman''s terms at all?  e.g. difference between class &
instant
> aspects.   (sorry - the penny hasn''t dropped yet :)  )
In layman''s terms, I''d describe it as, "A computer
programming thing"
:-)  But here''s a somewhat super-layman explanation.

Ruby has an attr_* family of methods:

   class C
     attr_accessor :x
     attr_reader :y
     attr_writer :z
   end

These attr_* methods are meta-methods; that is, calling them actually
results in the automatic creation of other methods.  In the example
above, instances of C will have the following methods:

   x     # reader
   x=    # writer
   y     # reader
   z=    # writer

The idea is to provide a convenient way to get and/or set state in an
object:

   c = C.new
   c.x = 1    # actually a call to the x= method!
   puts c.x   # a call to the x method

The way this works is that the reader and writer methods (x, x=, etc.)
store/retrieve values in/from instance variables.  If you wrote them
out, the methods that the attr_* methods create for you would look
like this:

   class C
     def x  # read "attribute" (i.e., value of instance variable)
       @x
     end

     def x=(value)  # set "attribute" (i.e., set instance variable)
       @x = value
     end

     def y
       @y
     end

     def z=(value)
       @z = value
     end
   end

In addition to instance variables, Ruby has class variables.  The
purpose of the cattr_* methods is to provide a mechanism exactly like
the above -- but using class variables instead of instance variables.
Furthermore, the set/get operations are available both to instances of
the class, and to the class itself:

   class D
     cattr_accessor :a
   end

   d = D.new
   d.a = 1     # set via an instance
   puts D.a    # get via the class

So it''s just a kind of elaboration of the original Ruby attribute
implementation.  To get both the class and its instances to know about
the get and set methods, there have to be two of each.  So this is
what the expanded version of the last example looks like:

   class D
     def self.a     # class get method
       @@a
     end

     def self.a=(value)  # class set method
       @@a = value
     end

     def a            # instance get method
       @@a
     end

     def a=(value)    # instance set method
       @@a = value
     end
   end

I personally consider "cattr" (class attribute) a misnomer.
"Attribute" suggests a property of an object.  Class variables do not
map onto the state of any particular object; they are visible to a
given class, all of its subclasses, and all of the instances of itself
and those subclasses.  So when you save a value in a class variable,
it''s a considerable stretch to refer to it as an "attribute".
But
anyway, the above is how it works and what it does.

David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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Rav Kir

2007-Dec-20 09:19 UTC

head link

Re: what is "cattr_accessor" (used in acts_as_audited)

In ruby core programs "cattr_accessor" method is not recognized (it
says
undefined method `cattr_accessor'').
I think you mean to say this method is available only in Rails, right?


example program -

class  Kcattr

cattr_accessor :var
@@var = 10

end
-- 
Posted via http://www.ruby-forum.com/.

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Kevin Skoglund

2007-Dec-20 16:03 UTC

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Re: what is "cattr_accessor" (used in acts_as_audited)

Yes, it is only in Rails.
/activesupport/lib/active_support/core_ext/class/
attribute_accessors.rb

It is set as "nodoc" though, so the definitions don''t show up
in the
API. (Any reason not to change that?)

Kevin

http://www.nullislove.com


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Shaun Br

2009-Sep-22 01:55 UTC

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Re: what is "cattr_accessor" (used in acts_as_audited)

David - thank you for taking the time to write down this explanation.
Helped me understand things. 3 years late but all the same.

Shaun

David Black wrote:
> 
> In layman''s terms, I''d describe it as, "A computer
programming thing"
> :-)  But here''s a somewhat super-layman explanation.
> 
> Ruby has an attr_* family of methods:
> 
>    class C
>      attr_accessor :x
>      attr_reader :y
>      attr_writer :z
>    end
> -- 
Posted via http://www.ruby-forum.com/.

Rails - Sep 2006 - what is "cattr_accessor" (used in acts_as_audited)

what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)

Re: what is "cattr_accessor" (used in acts_as_audited)