Rails - Aug 2006 - adding extra variable to a class, how to access it?

somple question here but pretty confusing on my side. i have a model 
towns that is mapped to my towns table. can i add an extra variable to 
the class and access it in my view? basicall what i am trying to do is 
return a list of towns, and next to each town, display a total number of 
what i have in each town.

ive tried both attr_reader and @total but no avail.

here is my view

   <% for county in @counties %>
      <h1><%= county.name %></h1>
      <% for town in county.towns %>
           <p><%= town.name %></p>
           <p><%= town.total %></p>

  <% end %>


my town model:

class Town < ActiveRecord::Base
  belongs_to :county
  attr_reader :total
  @total


  def self.get_list
    @total = 100
    find(:all)
  end
end

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never mind, i figured it out. i realized you can access instance 
variable directly, you need a ''get'' method.

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or attr_accessor :variable

Ross

On 8/12/06, koloa <none@none.com> wrote:
> never mind, i figured it out. i realized you can access instance
> variable directly, you need a ''get'' method.
>
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> Rails mailing list
> Rails@lists.rubyonrails.org
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>

-- 
Ross Riley
riley.ross@gmail.com

Ross Riley wrote:
> or attr_accessor :variable
> 
> Ross
Strangely enough, this does not work for me. I tried:

class Page < ActiveRecord::Base
  belongs_to :author
  attr_accessor :typus
end

and was not able to access somepage.typus in my view. However, this 
worked:

class Page < ActiveRecord::Base
  belongs_to :author
  def typus=(typus_value)
        write_attribute(:typus, typus_value)
  end

  def typus
    read_attribute(:typus)
  end
end

Why is it that attr_accessor does not work for an AR-based class?

Thanks,
Jan

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In addition to my recent message:

I can use somepage.typus (reading/writing) in the controller, but not 
read it in the view when using attr_accessor.


Jan Eden wrote:
> Ross Riley wrote:
>> or attr_accessor :variable
>> 
>> Ross
> 
> Strangely enough, this does not work for me. I tried:
> 
> class Page < ActiveRecord::Base
>   belongs_to :author
>   attr_accessor :typus
> end
> 
> and was not able to access somepage.typus in my view. However, this 
> worked:
> 
> class Page < ActiveRecord::Base
>   belongs_to :author
>   def typus=(typus_value)
>         write_attribute(:typus, typus_value)
>   end
> 
>   def typus
>     read_attribute(:typus)
>   end
> end
> 
> Why is it that attr_accessor does not work for an AR-based class?
> 
> Thanks,
> Jan

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Jan Eden schrieb:
> Ross Riley wrote:
>> or attr_accessor :variable
>>
>> Ross
> 
> Strangely enough, this does not work for me. I tried:
> 
> class Page < ActiveRecord::Base
>   belongs_to :author
>   attr_accessor :typus
> end
> 
> and was not able to access somepage.typus in my view. However, this 
> worked:
> 
> class Page < ActiveRecord::Base
>   belongs_to :author
>   def typus=(typus_value)
>         write_attribute(:typus, typus_value)
>   end
> 
>   def typus
>     read_attribute(:typus)
>   end
> end
> 
> Why is it that attr_accessor does not work for an AR-based class?
> 
> Thanks,
> Jan
> 
Hi Jan,

did you try to access a persistent or a non-persistent attribute?

What do you get when you @page.typus in your view, I guess nil unless
you''ve done something like @page.typus = ''something''
before...

Regards
Florian


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Florian Aßmann wrote:
> Jan Eden schrieb:
>> end
>>   def typus
>>     read_attribute(:typus)
>>   end
>> end
>> 
>> Why is it that attr_accessor does not work for an AR-based class?
>> 
>> Thanks,
>> Jan
>> 
> 
> Hi Jan,
> 
> did you try to access a persistent or a non-persistent attribute?
> 
> What do you get when you @page.typus in your view, I guess nil unless
> you''ve done something like @page.typus =
''something'' before...
> 
> Regards
> Florian
Hi Florian,

it''s a non-persistent attribute, calculated on the fly based on another
attribute (it''s actually a string to be used as a CSS classname).

@page.typus won''t work, because I use the instance variable @children
to
store a list of Page objects (which in turn have the typus attribute):

This is what happens in the controller:

@children = Page.find(:all, :conditions => "mother_id =
#{page.id}",
:order => "position asc, title asc")
    @children.each do |child|
      child.author = nil if child.author == page.author
      child.typus = (child.visible_children != nil) ? ''Node'' :
''Page''
    end

This does set @typus for each child page correctly (I inspected the 
children), but I cannot access the instance variable (like child.typus) 
when doing only "attr_accessor :typus" in the model.

Thanks,
Jan



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Hi Jan
>     @children.each do |child|
>       child.author = nil if child.author == page.author
>       child.typus = (child.visible_children != nil) ?
''Node'' : ''Page''
>     end
In this case I''d drop

  child.typus = (child.visible_children != nil) ? ''Node'' :
''Page''

and def typus in the model itself:

  def typus
    visible_children ? ''Node'' : ''Page''
  end

What''s your code in the view? I can''t understand why accessor
shouldn''t
work...

Regards Florian


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Florian Aßmann wrote:
> Hi Jan
> 
>>     @children.each do |child|
>>       child.author = nil if child.author == page.author
>>       child.typus = (child.visible_children != nil) ?
''Node'' : ''Page''
>>     end
> 
> In this case I''d drop
> 
>   child.typus = (child.visible_children != nil) ? ''Node''
: ''Page''
> 
> and def typus in the model itself:
> 
>   def typus
>     visible_children ? ''Node'' : ''Page''
>   end
> 
> What''s your code in the view? I can''t understand why
accessor shouldn''t
> work...
Thanks for the suggestion, that''s definitely an improvement (and it 
works fine).

The view simply has:

<% @children.each do |child| %>
  <li><a class="<%= child.typus %>"
href="/pages/<%= child.id %>.html"
target="_self"><%= child.title %></a></li>
</end>

To summarize:

- your suggestion (a simple method for each Page instance) works
- The AR-specific getter/setter methods using 
write_attribute/read_attribute work
- The generic attr_accessor method to create an attribute does not work 
(Error: undefined method)

Thanks again,
Jan

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I''m very curious about this one. For me, declaring accessors, has
always
worked in my whole rails code...

The objects in children in your view are really instances of Page? Did
you make a child.inspect in vour view or child.methods.sort or maybe
even child.instance_variable_get(:@typus)?

I use inspect and methods(+grep) very often at frontend debugging...

Regards
Florian

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Florian Aßmann wrote:
> I''m very curious about this one. For me, declaring accessors, has
always
> worked in my whole rails code...
> 
> The objects in children in your view are really instances of Page? Did
> you make a child.inspect in vour view or child.methods.sort or maybe
> even child.instance_variable_get(:@typus)?
> 
> I use inspect and methods(+grep) very often at frontend debugging...
> 
> Regards
> Florian
Ok, here''s a simplified version of my setup (the model lists the three 
variants of implementing an attribute, of which variant 1) does not 
work):

## Model:

class Page < ActiveRecord::Base
  belongs_to :author

  # 1)
  # attr_accessor :typus

  # 2)
  # def typus=(typus_value)
  #       write_attribute(:typus, typus_value)
  # end
  #
  # def typus
  #   read_attribute(:typus)
  # end

  # 3)
  # def typus
  #   visible_children ? ''Knoten'' : ''Seite''
  # end

end

The controller needs to iterate over each child for variants 2) and 3)

## Controller:

class PagesController < ApplicationController

  def index
    page = Page.find(:first, :conditions => "id =
#{params[''id'']}")
    @title = page.title
    @content = page.content
    @children = Page.find(:all, :conditions => "mother_id =
#{page.id}",
:order => "position asc, title asc")

          # @children.each { |child| child.typus = 
child.visible_children ? ''Knoten'' : ''Seite''
}
  end

end

The view simply uses child.typus for each element of @children:

## View:

<h1><%= @title %></h1>

<%= @content %>

<% @children.each do |child| %>
  <li><a class="<%= child.typus %>"
href="/pages/<%= child.id %>.html"
target="_self"><%= child.title %></a></li>
<% end %>

Cheers,
Jan

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