Running only paperclip validations in Rails

Question

I've model Profile

class Profile < Abstract
    has_attached_file :avatar,                   
    ...
    validates_attachment_size :avatar, :less_than => 2.megabytes
    validates_attachment_content_type :avatar, :content_type => ['image/jpeg', 'image/png', ...]
    # Many other validations
end

I have two different forms: one for avatar and another for all other fields. User have to be able to save avatar without filling second form. Is it possible to validate only paperclip attachment, skipping all other validations? Following this answer I tried to do like this:

class Abstract < ActiveRecord::Base  
    def self.valid_attribute?(attr, value)
        mock = self.new(attr => value)
        unless mock.valid?
           return !mock.errors.has_key?(attr)
        end
        true
    end
end

and in controller

def update_avatar
    if params[:profile] && params[:profile][:avatar].present? && Profile.valid_attribute?(:avatar, params[:profile][:avatar])
        @profile.avatar = params[:profile][:avatar]
        @profile.save(:validate => false)
        ...
    else
        flash.now[:error] = t :image_save_failure_message
        render 'edit_avatar'
    end
end

But it didn't work for paperclip. Profile.valid_attribute?(:avatar, params[:profile][:avatar]) always returns true.

Answer 1

Instead of trying to do all this magic, create a separate Image or Avatar model that is going to be your image model, as in:

class Attachment < ActiveRecord::Base

  belongs_to :owner, :polymorphic => true

  has_attached_file :file,
                :storage => :s3,
                :s3_credentials => "#{Rails.root}/config/s3.yml",
                :s3_headers => {'Expires' => 5.years.from_now.httpdate},
                :styles => { :thumbnail => "183x90#", :main => "606x300>", :slideshow => '302x230#', :interview => '150x150#' }

  def url( *args )
    self.file.url( *args )
  end

end

Once you have this, create the relationship:

class Profile < Abstract
  has_one :attachment, :as => :owner, :dependent => :destroy
end

Then, at your form, you save the attachment first, independent of your model, and then try to save the profile setting the attachment to it. Could be something like this:

def create

  @attachment = if params[:attachment_id].blank?
    Attachment.create( params[:attachment )
  else
    Attachment.find(params[:attachment_id])
  end

  @profile = Profile.new(params[:profile])
  @profile.image = attachment unless attachment.new_record?
  if @profile.save
    # save logic here
  else
    # else logic here
  end 
end

Then, at your view, in the case the profile was invalid, you send the newly saved attachment to the form and just reuse it instead of having to create it again.