Rails Paperclip多态风格

Question

I'm using paperclip for attachments for multiple models using accepts_nested_attributes_for. Is there a way I can specify specific paperclip style options for each model?

Answer 1

Yes. I use single table inheritance (STI) on sites for handling Audio, Video, and Images via an Asset model.

# models/Asset.rb
class Asset < ActiveRecord::Base
  # Asset has to exist as a model in order to provide inheritance
  # It can't just be a table in the db like in HABTM. 
end

# models/Audio.rb
class Audio < Asset # !note inheritance from Asset rather than AR!
  # I only ever need the original file
  has_attached_file :file
end

# models/Video.rb
class Video < Asset
  has_attached_file :file, 
    :styles => {
      :thumbnail => '180x180',
      :ipod => ['320x480', :mp4]
      },
    :processors => "video_thumbnail"
end

# models/Image.rb
class Image < Asset
  has_attached_file :file,
    :styles => {
      :medium => "300x300>", 
      :small => "150x150>",
      :thumb => "40x40>",
      :bigthumb => "60x60>"
    }
end

They all come into Rails as :file , but the controller (A/V/I) knows to save to the proper model. Just remember that all attributes for any of the forms of media need to be included in Asset : if video doesn't need captions but images do, then the caption attribute will be nil for Video . It won't complain.

Associations will also work fine if hooked up to the STI models. User has_many :videos will operate the same as you are using it now, just make sure you don't try to save to Asset directly.

  # controllers/images_controller.rb
  def create
    # params[:image][:file] ~= Image has_attached_file :file
    @upload = current_user.images.build(params[:image]) 
    # ...
  end

Lastly, since you do have an Asset model, you can still read directly from it if eg you want a list of the 20 most recent Assets. Also, this example isn't restricted to separating media types, it can be used for different kinds of the same thing as well: Avatar < Asset, Gallery < Asset, and so on.

Answer 2

A much nicer way can be, (if use are dealing with images):

class Image < ActiveRecord::Base
  belongs_to :imageable, :polymorphic => true
  has_attached_file :attachment, styles: lambda {
    |attachment| { 
      thumb: ( 
        attachment.instance.imageable_type.eql?("Product") ? ["300>", 'jpg'] :  ["200>", 'jpg']   
      ),
      medium: ( 
       ["500>", 'jpg']
      )
    }
  }
end