Aliasing Active Record Attributes (also delegation issues)

[Tyler Prete]

This whole situation is a mess, but I'll see if I can explain it well.

I have two models, User and Company.  I'd like user to be able to get company.name.  I'm aware of the problems with using @ user.company.name, because of company is nil, then name throws an error.

So originally, I wrote this method instead

class User
  def company_name
    company ? company.name : nil
  end
end

This works, however, rather than use that, I would like to use delegation.  The problem I ran into with that,
however, is that user also has a name.  So I can't simply write

class User
  delegate :name, :to => :company
end

because that will overwrite name.  It would be nice if there was a delegate :company_name, :as => :name, :to => :company, but as far as I know this doesn't exist.  So... I thought I would use "delegate :company_name: to => :company", and alias :company_name to :name within company, like so:

class Company
  alias :company_name :name
end

however, that will not work with Active Record models, because name is not defined until the class is instantiated.  I could just write a wrapper method, aka def class_name; name; end; but that adds an extra method call that I'd rather not have.  So finally, I came up with this solution:

class Company
  def company_name
    name
    self.class.class_eval do
      alias_method :company_name, :name
    end
    name
  end
end


This works, because the first time company_name is called, it calls name to instantiate it (needed the first call for some reason), then it opens the class and aliases company_name to name.  Lastly, it returns name, so that it works as intended on the first call as well.
This code does work, I have tested it, but it seems like an awful lot of work for what seems like a simple concept.  Maybe I'm just making things too complicated, and should have simply used my company_name method within User, I don't know.

If anyone can suggest a better way to solve this problem, it would be much appreciated.

Thanks,
Tyler Prete

[augustl...@gmail.com]

I'm not entirely sure, but i think @object.content.name only trows an
error if @object.content is nil AND you're in development mode (whiny
nils is enabled). Not sure though.

[Chris Wanstrath]

On 1/20/07, Tyler Prete <psy...@gmail.com> wrote:

> class Company
> alias :company_name :name
> end

class Company
alias_attribute :company_name, :name
end

--
Chris Wanstrath
http://errtheblog.com

[Tyler Prete]

Chris,

Thanks!  Much much better.  I had the feeling that there had to be a better way, and there it is.

--Tyler

P.S.  I really like your blog.  Lots of good information on there.