Rails - Jul 2006 - weird result for a custom attr reader!

Hi all,

I am having a weird problem reading a value from my model. basicaly, I 
have these two models:

class Category < ActiveRecord::Base
  acts_as_tree :order => "name"
  belongs_to :item_type
  has_many :specific_category_names
end

and

class SpecificCategoryName < ActiveRecord::Base
  set_table_name "Specific_category_names"

  has_many :products
  belongs_to :brand
  belongs_to :category

  #if there is no name, use the name of the category
  def name
    if @name.nil?
      category.name
    else
      @name
    end
  end
end

Then, I start to play in the console... In my DB, 
specific_category_names.name for canon is = "WIDER" and the 
corresponding category.name = "wide"
>>canon = Brand.find_by_name("Canon")
=>#<Brand:0x2429784 @attributes={"name"=>"Canon",
"id"=>"1"}>

Thats OK
>>canon.specific_category_names.first
=>#<SpecificCategoryName:0x24235a0
@attributes={"name"=>"WIDER",
"brand_id"=>"1", "id"=>"1",
"description"=>nil, "category_id"=>"7"}>

then the strange things:
>> canon.specific_category_names.first.name
=> "Wide"
This should be "WIDER" since that the value from
specific_category_name
and it is not null!!!


And even weirder, if I ask again for the specific_category_name array, I 
will get the same one as before but this time there is a @category 
added...
>> canon.specific_category_names.first 
=> #<SpecificCategoryName:0x24235a0
@attributes={"name"=>"WIDER",
"brand_id"=>"1", "id"=>"1",
"description"=>nil, "category_id"=>"7"},
@category=#<Category:0x241557c
@attributes={"name"=>"Wide",
"id"=>"7",
"description"=>nil, "item_type_id"=>"1",
"parent_id"=>"2"}>>


Anyone can tell me what I am doing wrong?!? This is puzzling me to no 
end!

Thanks

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

"Alain Pilon" <mantat@videotron.ca> wrote in 
message
news:6cf85b3b19dbca955acfe62c2add9d0d@ruby-forum.com...
> Hi all,
>
> I am having a weird problem reading a value from my model. basicaly, I
> have these two models:
>  #if there is no name, use the name of the category
>  def name
>    if @name.nil?
>      category.name
>    else
>      @name
>    end
>  end
> end
ActiveRecord attributes aren''t stored as instance variables in the
model so
you don''t need the @. I''m pretty sure AR uses method_missing
to return
attribute values, try something like this:

def name
  tmp = super
  return tmp || category.name
end

I think (ie untested) you should be able to use

def name
  self[:name] || category.name
end

See "Overwriting default accessors" in
http://api.rubyonrails.com/classes/ActiveRecord/Base.html

Chris

On 7/19/06, Alan Bullock <liststuff@gmail.com>
wrote:
> "Alain Pilon" <mantat@videotron.ca> wrote in
> message news:6cf85b3b19dbca955acfe62c2add9d0d@ruby-forum.com...
> > Hi all,
> >
> > I am having a weird problem reading a value from my model. basicaly, I
> > have these two models:
> >  #if there is no name, use the name of the category
>
> >  def name
> >    if @name.nil?
> >      category.name
> >    else
> >      @name
> >    end
> >  end
> > end
>
> ActiveRecord attributes aren''t stored as instance variables in the
model so
> you don''t need the @. I''m pretty sure AR uses
method_missing to return
> attribute values, try something like this:
>
> def name
>   tmp = super
>   return tmp || category.name
> end
>
>
>
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

Thx Chris, that solved my problem. But why use self[:name] and not 
self.name ???

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

self[:name] is essentially the rails equivalent of @name.

if you tried to use self.name, you would invoke the name method on the
current instance, from within... the name method on the current
instance; resulting in an infinite loop

On 7/20/06, Alain Pilon <mantat@videotron.ca>
wrote:
> Thx Chris, that solved my problem. But why use self[:name] and not
> self.name ???
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

On 7/20/06, Chris Roos <chrisjroos@gmail.com>
wrote:
> self[:name] is essentially the rails equivalent of @name.
In ruby, this isn''t necessarily true, as @name, self[:name] and
self.name can all be different:

irb(main):001:0> class A
irb(main):002:1>  def initialize
irb(main):003:2>   super
irb(main):004:2>   @p = 2
irb(main):005:2>  end
irb(main):006:1>  def [] y
irb(main):007:2>   @x ||= {}
irb(main):008:2>   @x[y]
irb(main):009:2>  end
irb(main):010:1>  def p
irb(main):011:2>   1
irb(main):012:2>  end
irb(main):013:1>  def test
irb(main):014:2>   puts "@p = #{@p}"
irb(main):015:2>   puts "self.p = #{self.p}"
irb(main):016:2>   puts "self[:p] = #{self[:p]}"
irb(main):017:2>  end
irb(main):018:1>  def self.test
irb(main):019:2>   new.test
irb(main):020:2>  end
irb(main):021:1> end
=> nil
irb(main):022:0> A.test
@p = 2
self.p = 1
self[:p] => nil

For ActiveRecord objects, self[:blah] and self.blah are usually the
same if blah is a column in the associated table (since self.blah will
default to self[:blah]), but that can be (and often is) changed.
However, ActiveRecord doesn''t create @blah instance variables for
columns, AFAIK.

Jeremy