Overriding initialize without causing infinite loop

R Mason wrote:

This might be more of a general Ruby question than a Rails question.

I have a model Upload, with subclasses such as Image, Video, Document,
etc; that way I could check what type of file has been uploaded and
create the relevant object, and based on what object it is, make a
thumbnail or screencap or excerpt, whatever.

What I wanted to do is something along the lines of "upload =
Upload.new(params[:upload])" within the controller, and then override
Upload's initialize method so it's something like:

I would suggest creating a new class method for Upload, say new_for().
For example,

def Upload.new_for(attributes)
    case attributes[:file].content_type
    when /^image/
        return Image.new(attributes)
    when /^video/
        return Video.new(attributes)
    when /^doc/
        return Document.new(attributes)
    end
    nil
end

Then use upload = Upload.new_for(params[:upload]) instead.

--Long
http://MeandmyCity.com/
http://edgesoft.ca/blog/read/2

R - you are correct in wanting to get it right from the start but using
"initialize" in your approach won't work. I am with Mark and Long on
this. This is the object oriented way of doing it.

This allows you to instantiate the proper class based on some outside
information. On the other hand, when you *know* you want to create an
Image object you just call Image.create directly.

By the way, Upload should be an abstract superclass and never
instantiated. You can specify this in rails by adding the following
line to your Upload model:

    self.abstract_class = true

However, don't use abstract_class if you are using Single Table
Inheritance (STI).

-Paul

How about something like this?

  class Upload # a PORO, not an AR::Base subclass
    def initialize(attributes
      ...
      @asset = Image.new(...)
      ...
    end
  end

  class Asset < ActiveRecord::Base
    ...
  end

  class Image < Asset
    ...
  end

Michael