Fallback Image with Carrierwave - ruby-on-rails

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