What is wrong with my heroku asset:compilation? - ruby-on-rails

Question

I am trying to insert an image into a mailer, everything runs locally but heroku doesn't see the image on its server despite pushing and precompiling as I'm ought to do. Code as below;
user_mailer.rb
def welcome_email(user)
#user = user
attachments.inline['my_logo_sml.png'] = File.read('app/assets/images/my_logo_sml.png')
mail(to: #user.email, subject: 'Welcome to Mybiz')
end
welcome_email.html.erb
<td class="six sub-columns header_logo">
<%= image_tag attachments["my_logo_sml.png"].url -%>
</td>
gemfile
gem 'rails_12factor', group: :production
app/assets/images/my_logo_sml.png is clearly present and getting through the pipline locally.
I have run RAILS_ENV=production bundle exec rake assets:precompile a number of times, I have heroku restart'ed a number of times.
Heroku logs:
2015-06-03T22:38:50.824191+00:00 app[web.1]: Errno::ENOENT (No such file or directory # rb_sysopen - app/assets/images/my_logo_sml.png)
I'm at a loss after hours going round and around on this, can anyone help me please?
Update
After hours of looking at this i feel like it's not a syntax issue but an asset pre-compilation issue of some sort, I've copied my config/environments/production.rb code below if anyone can spot anything wrong?:
Rails.application.configure do
config.cache_classes = true
config.eager_load = true
config.consider_all_requests_local = false
config.action_controller.perform_caching = true
config.serve_static_files = ENV['RAILS_SERVE_STATIC_FILES'].present?
config.assets.js_compressor = :uglifier
config.assets.compile = true #concerned that this is the right thing to do?
config.assets.digest = true
config.log_level = :debug
config.i18n.fallbacks = true
config.active_support.deprecation = :notify
config.log_formatter = ::Logger::Formatter.new
config.active_record.dump_schema_after_migration = false
config.action_mailer.asset_host = 'http://mysite.co'
ActionMailer::Base.smtp_settings = {
:address => 'smtp.sendgrid.net',
:port => '587',
:authentication => :plain,
:user_name => ENV['SENDGRID_USERNAME'],
:password => ENV['SENDGRID_PASSWORD'],
:domain => 'heroku.com',
:enable_starttls_auto => true
}
end
Perhaps I could clean all compiled assets out and start the whole thing again, could anyone advise as to how to do this?
Update
The source of my problem seemed to be confusion between local and slug asset compilation. I ran heroku run rake assets:clobber and this solved all of my problems. Full understanding of what precisely was going on still eludes me, however running the above and having config.assets.compile = true in config/environments/production.rb has everything working just fine and upon git push heroku it shows me clearly that it's running both rake assets:clean and rake assets:precompile just fine. Syntax used in the view was:
welcome_email.html.erb
<%= image_tag('my_logo_sml.png', alt: "My Logo Small")%>
I'm still unsure as to whether having config.assets.compile = true is the correct thing to do despite it seeming to solve the problem, i wonder whether it might end up compiling assets on multiple occasions?

Answer 1

I had similar problem. I think welcome_email.html.erb file can not be .erb file. There is a workaround. You can put image somewhere on the web like Amazon or Image share services and use link as source.
<img src='https://example.com'>

Answer 2

Reading the file from Rails console as suggested by #user123 shows that the paths are correct and the file is there. Trying to reading the file from Heroku run console does not find the file and comes up with the same Errno::ENOENT no such file error Strangely heroku is serving an image in the homepage which i try to load as described above in heroku console and it is unable to find it.