Models with attachments and one AttachmentsController: how?

Rails
1

First off, I beg your pardon for the somewhat cryptic topic, but I
couln’t think of anything better.

The issue I’m facing is that I have some models (User, Product, Maker)
which can have one or more
attachments:

A User has_one avatar
A Maker has_one logo
A Product has_many pictures, and has_many documents

“Avatar”, “logo” and “documents” are all aliases for a model named
“Attachment” and, thus, the
aforementioned relations are all polymorphic.

I’m using “attachment_fu” plugin to handle attachments.

While writing the code I’ve found that there are many such constructs
repeating all over:

def update
flash[:error] = “couldn’t update product” unless
@product.update_attributes(params[:product])
if !params[:attachment].blank?
flash[:error] = “couldn’t add the attachment” unless
@product.attachments << Attachment.create(params[:attachment])
end
redirect_to edit_product_path(@product)
end

This smells a lot. I thought there should be one controller in charge of
handling attachments, namely
AttachmentsController, so far so good.

But…since the AttachmentsController would be “REST style”, it will
only have one “create” action which
will be used in different contexts (User, Product, Maker).
Create action will be passed the usual “params” hash built like this:
:xxxxx_id => 1, :uploaded_data => “…”

Where “xxxxx_id” will be replaced by “user_id”, “product_id” and
“maker_id” depending on the what
model I’m creating attachment for.

Being params: :user_id => 1, :uploaded_data => “some stuff”

I thought the AttachmentsController#create action should look like:

context = params.keys.find do |k| k.to_s =~ /._id/ end
class_type = eval(context.to_s.gsub(/._id/,’’).classify)
instance = class_type.find(params[context])
instance.attachments.create(params[:uploaded_data])

Is that a correct way to proceed, or there’s an easier and cleaner way?

Thanks in advance for your help

Regards,
Carmine

2

what you’re describing is a polymorphic association.

3

Hi Jeff,

Jeff Emminger wrote:

what you’re describing is a polymorphic association.
ActiveRecord::Associations::ClassMethods

Indeed, Attachment is associated polymorphically to the other models.

What I want to accomplish is removing code duplication from some of the
controllers.
Let’s say I have:

  • User has_one :attachment, :as => :attachable
  • Maker has_one :attachment, :as => :attachable
  • Product has_many :attachments, :as => :attachable

Now, in their respective controllers, the “update” action looks like
this:

def update
flash[:error] = “couldn’t update product” unless
@product.update_attributes(params[:product])
if !params[:attachment].blank?
flash[:error] = “couldn’t add the attachment” unless
@product.attachments << Attachment.create(params[:attachment])
end
redirect_to edit_product_path(@product)
end

The “interesting” part is the one where the Attachment gets created and
associated to its “owner” (in
that case, the Product).

This part is repeated also in the UsersController and MakersController.

I thought that, trying to comply to the “everything is a resource”
mantra, I should move that part outside the afore mentioned controllers
and in a controller of its own. Say: AttachmentsController.

Routes are set as follows:

map.resources :users do |user|
user.resource :attachment, :controller => ‘attachments’
end

map.resources :makers do |maker|
maker.resource :attachment, :controller => ‘attachments’
end

map.resources :products do |product|
product.resources :attachments, :controller => ‘attachments’
end

This leads to a problem.
User, maker and products “edit” view will have to use
AttachmentsController in order to create
a new attachment for their respective model. Hence, they will all call
AttachmentsController#create action passing parameters.

To solve this problem, I thought of implementing the “create” action
that way:

context = params.keys.find do |k| k.to_s =~ /._id/ end
class_type = eval(context.to_s.gsub(/._id/,‘’).classify)
instance = class_type.find(params[context])
instance.attachments.create(params[:uploaded_data])

And the question is:
is it correct to have AttachmentsController handle the attachments of
user, maker and product models, or should I stick with the shown
“update” action and let UsersController, MakersController and
ProductsController handle the attachments?

Now, I beg your pardon if I’ve been unclear (my english is worse than my
code :slight_smile: ).

Thanks for your help

4

And the question is:
is it correct to have AttachmentsController handle the attachments of
user, maker and product models, or should I stick with the shown
“update” action and let UsersController, MakersController and
ProductsController handle the attachments?

It’s correct in my opinion… you have only one place to maintain the
attachment code.