rails 3与回形针和多个模型的多态关联

Question

I want to make polymorphic associations with paperclip, and allow my user to have one avatar and multiple images.

Attachment model:

class Attachment < ActiveRecord::Base
belongs_to :attachable, :polymorphic => true
end

class Avatar < Attachment
has_attached_file :image, :styles => { :thumb => "150x150>", :view => "260x180>" },
end

class Image < Attachment
has_attached_file :image, :styles => { :thumb => "150x150>", :view => "260x180>" },
end

User Model:

has_one :avatar, :as => :attachable, :class_name => 'Attachment', :conditions => {:type => 'avatar'}
accepts_nested_attributes_for :avatar

User Controller:

def edit
   @user.build_avatar
end

User View form:

<%= form_for @user, :html => { :multipart => true } do |f| %>

  <%= f.fields_for :avatar do |asset| %>
      <% if asset.object.new_record? %>
          <%= asset.file_field :image %>
      <% end %>
  <% end %>

when I attempt to save the changes I get the error => unknown attribute: avatar

if I remove the :class_name => 'attachment' in the has_one association I get the error => uninitialized constant User::Avatar

I need to also attach avatars to blog posts, so I need the association to be polymorphic (or atleast i think so)

I am stumped and any help would be greatly appreciated.

Answer 1

I do have a project in the works that is successfully using Paperclip and polymorphic associations. Let me show you what I have, and maybe you can apply it to your project:

class Song < ActiveRecord::Base
  ...
  has_one :artwork, :as => :artable, :dependent => :destroy
  accepts_nested_attributes_for :artwork
  ...
end

class Album < ActiveRecord::Base
  ...
  has_one :artwork, :as => :artable, :dependent => :destroy
  accepts_nested_attributes_for :artwork
  ...
end

class Artwork < ActiveRecord::Base
  belongs_to :artable, :polymorphic => true
  attr_accessible :artwork_content_type, :artwork_file_name, :artwork_file_size, :artwork

  # Paperclip
  has_attached_file :artwork,
    :styles => {
      :small => "100",
      :full => "400"
    }

  validates_attachment_content_type :artwork, :content_type => 'image/jpeg'
end

the songs form and the albums form include this as a partial:

<div class="field">
<%= f.fields_for :artwork do |artwork_fields| %>
  <%= artwork_fields.label :artwork %><br />
  <%= artwork_fields.file_field :artwork %>
<% end %>

don't forget to include :html => { :multipart => true } with the form

artworks_controller.rb

class ArtworksController < ApplicationController
  def create
    @artwork = Artwork.new(params[:artwork])

    if @artwork.save
        redirect_to @artwork.artable, notice: 'Artwork was successfully created.'
    else
        redirect_to @artwork.artable, notice: 'An error ocurred.'
    end
  end
end

and finally, an excerpt from songs_controller.rb:

def new
    @song = Song.new
    @song.build_artwork
end

Answer 2

I'm not sure you really need to be polymorphic. How about this approach, which uses has_many :through? In plain English, the user has one avatar which has multiple images, and through this association you can call User.images to get the collection of images associated with the avatar.

http://guides.rubyonrails.org/association_basics.html

class User < ActiveRecord::Base
  has_one :avatar
  has_many :images, :through => :avatar
end

class Avatar < ActiveRecord::Base
  belongs_to :user
  has_many :images
end

class Image < ActiveRecord::Base
  belongs_to :avatar
  has_attached_file :image, :styles => { :thumb => "150x150>", :view => "260x180>" },
end

Having said all of this, I am left to wonder why you need to go through all this anyway. Why not just do

class User < ActiveRecord::Base
  has_many :avatars
end

which would give you as many images (avatars) as you want.