Rails - Nov 2006 - redefining the method belongs_to in ActiveRecord::Base

Hi. I''ve tried to redefine the method belongs_to in ActiveRecord::Base,
so every time a model is defined as belonging to :attachment, it should
have some additional methods. I tried to do an alias of belongs_to, but
this was not successful. The error message in Webrick was
> Booting WEBrick...
./script/../config/../lib/ActiveRecordExtensions.rb:67: undefined
method `belongs_to'' for module `ActiveRecord'' (NameError)

The code with problem is:

  alias :attachment_belongs_to :belongs_to
  def belongs_to(association_id, options={})
    self.attachment_belongs_to(association_id,options)
    if association_id == :attachment

     code = <<EOS
  alias :tmp_attach= :attachment  def attachment=(content)
    if content.class.name == ''Attachment'' #old functionality
      self.tmp_attach=(content)
    else
      if content.class.name.match(/^Hash/) &&
content["content"] &&
content["content"].original_filename != ""
        if self.attachment
          self.attachment.update_attributes(content)
        else
          attach = Attachment.new(content)
          attach.save
          self.tmp_attach=(attach)
        end
      end
    end
  end

  alias :tmp_destroy :destroy
  def destroy
    attach = self.attachment
    self.tmp_destroy
    attach.destroy if attach
  end      
EOS
      module_eval(code)
    
    end
  end


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Hi --

On Thu, 9 Nov 2006, Vinicius  Cubas Brand wrote:
>
> Hi. I''ve tried to redefine the method belongs_to in
ActiveRecord::Base,
> so every time a model is defined as belonging to :attachment, it should
> have some additional methods. I tried to do an alias of belongs_to, but
> this was not successful. The error message in Webrick was
>
>> Booting WEBrick...
> ./script/../config/../lib/ActiveRecordExtensions.rb:67: undefined
> method `belongs_to'' for module `ActiveRecord'' (NameError)
>
> The code with problem is:
>
>  alias :attachment_belongs_to :belongs_to
I suspect the problem was actually before this.  It sounds like you
had:

   module ActiveRecord

when you wanted:

   class ActiveRecord::Base

(I haven''t looked at the rest of the code in detail but I think
that''s
what''s triggering this error.)


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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unknown wrote:
> Hi --
> 
> On Thu, 9 Nov 2006, Vinicius  Cubas Brand wrote:
> 
>> The code with problem is:
>>
>>  alias :attachment_belongs_to :belongs_to
> 
> I suspect the problem was actually before this.  It sounds like you
> had:
> 
>    module ActiveRecord
> 
> when you wanted:
> 
>    class ActiveRecord::Base
> 
> (I haven''t looked at the rest of the code in detail but I think
that''s
> what''s triggering this error.)
I suspect this is correct.  Also belongs_to is a class method and must 
be declared as such.  You can also define you own class that 
enscapsulates this through inheritance, which has the advantage of 
calling to original functionality through a clean ans slick call to 
"super"

  class Foo < ActiveRecord::Base
    self.abstract_class = true # tell AR there is no table for this 
class
    def self.belongs_to(*args)
      if args[0] == ''something''
        super(*args) # do whatever AR does normally
      else
        do_something_custom
      end
    end
  end

  class MyModel < Foo
    belongs_to :bar
  end

In my experience inheritance is the cleanest way to extend an existing 
complex class with non standard functionality and just feels more right 
than some method aliasing hack around a method.

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

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