Question

I’m working on upgrading an app to Rails 3, and attachment_fu is broken so I’m moving to carrierwave. Is there a systematic process that I can go through to upgrade from attachment_fu to carrierwave? Or a tutorial for it? Right now, I’m more interested in getting everything on the database end right. I’m using the filesystem store option for attachment_fu and carrierwave.

I’ve found a module, UploaderFu from http://ruby.simapse.com/2011/03/migrate-attachmentfu-to-carrierwave.html that tells carrierwave to use the same directories and filenames as attachment_fu. But it’s not the entire answer, just part of it.

For example, in the db, I have a UserImage model, with :filename, :content_type, :size, :width, :height, and :user_id attributes. I added a :user_avatar column, and the following to my model

attr_accessible :user_avatar
mount_uploader :user_avatar, UserAvatarUploader

What exactly gets stored in :user_avatar. Is it just the filename? or something else? Do I just need to write a migration to move the data in :filename (stored like "hello_world.png") to :user_avatar? If that’s the case I should just use the original :filename instead of creating a :user_avatar column, right?

Answer 1

The column you mount the uploader on is supposed to store an “identifier” for the uploaded file. By default it’s just the filename, but you can override it to be almost anything apart from the ID of the record (because you can’t know what that is until after saving).

To override: in your uploader class, add this definition :

def identifier
       # This is what gets put in the database column!
       model.created_on
end

In this example I’ve used the created_on attribute from the model. If you want to create your own storage mechanism then you need to be able to uniquely identify files by this identifier so be careful what you choose.

I would suggest renaming the column so it describes the file that’s being uploaded (like in the carrierwave example). Then you can always change the identifier from filename to something else later.