Fallback Image with Carrierwave

Question

My uploader is working well apart from one small thing. The setting of default images. I'm using carrierwave for users to upload profile images of themselves:

user model

class User < ActiveRecord::Base     
    has_one :avatar, class_name: 'Image', foreign_key: :user_id

    before_create :create_fallback_image

    def create_fallback_image
        self.create_avatar
    end
end

image model

class Image < ActiveRecord::Base

    mount_uploader :file_name, AvatarUploader, auto_validate: false

    belongs_to :user
end

avatar uploader

class AvatarUploader < BaseUploader

  include CarrierWave::RMagick

  storage :file

  process resize_to_fit: [75, 75]
  process convert: 'gif'

  def default_url
   'foobar'
  end

  def filename
      random_string + '.gif'
    end
  end

  def random_string
    @random_string ||= User.random_string
  end
end

When a user signs up without uploading an optional profile image, they are assigned an association to their profile image, but instead of the default_url working, they get a random string from the filename method.

I thought I could get around it like this:

user model

class User < ActiveRecord::Base     
    has_one :avatar, class_name: 'Image', foreign_key: :user_id

    before_create :create_fallback_image

    def create_fallback_image
            # look here:

        self.create_avatar.create_fallback
    end
end

image model

class Image < ActiveRecord::Base

    mount_uploader :file_name, AvatarUploader, auto_validate: false

    belongs_to :user

    def create_fallback
       self.update_attributes(file_name: 'my_fallback.jpg')
    end
end

and while it nearly, nearly works, when I update the attributes of the file_name column, the uploader kicks in and my_fallback.jpg is overridden by a random string from my random_string method!

Answer 1

Carrierwave has a built-in fallback mechanism for default image

Update your default_url method in AvatarUploader as below:

  def default_url
    ActionController::Base.helpers.asset_path("fallback/" + [version_name, "my_fallback.jpg"].compact.join('_'))
  end

where change fallback/ to your desired folder path. This way, when an avatar is not uploaded for a particular user then my_fallback.jpg would be used as fallback image.

Refer to section Providing a default URL in Carrierwave Documentation.

when I update the attributes of the file_name column, the uploader kicks in and my_fallback.jpg is overridden by a random string from my random_string method!

This happens because you have overridden filename method in AvatarUploader which gets called every time an image is uploaded. If you notice, its calling random_string method in it. Hence, you get a random string as your filename.

UPDATE

As per the chat session with OP, if an avatar is not uploaded for a user then a default image should be shown. I suggested the following helper :

module ApplicationHelper
  def display_avatar(user)  
    unless user.avatar.nil? 
      image_tag(user.avatar.file_name) 
    else
      image_tag("/path/to/fallback.jpg")
     end    
  end
  ## ...
end

Use this helper method in views to display avatar image appropriately.

Answer 2

Also, you can do it within model:

class User < ApplicationRecord
  has_one :avatar, class_name: 'User::Avatar', as: :parent, dependent: :destroy
  accepts_nested_attributes_for :avatar, allow_destroy: true #, ...

  def avatar
    super || build_avatar
  end
end