rails carrierwave + S3 + json response - ruby-on-rails

Question

I have a rails4 app that using carrierwave with S3 and cloudfront. I only have problem with the fallback image. When I'm using html response (<%= image_tag user.profile.avatar.url(:base_thumb), class: "profile-index-avatar" %>) with the helper everything works fine, but can't figure it out how to make it work with json response.
If I check out the html (built from json) in production on the root page the code is:
1st jbuilder: <img src="https://example.com/small_thumb_default.png">
2st jbuilder: <img src="https://example.com/assets/small_thumb_default.png">
None of these are working.
On the top of this if I go let's say to the users page then it tries to get pic like:
1st jbuilder: <img src="https://example.com/users/small_thumb_default.png">
2nd jbuilder: <img src="https://example.com/users/assets/small_thumb_default.png">.
What should I change?
jbuilder 1st version
json.array! #other_notifications do |notification|
..
json.profile_image_url notification.sender.profile.avatar.url(:small_thumb)
...
end
jbuilder 2nd version
json.array! #other_notifications do |notification|
..
if notification.sender.profile.avatar_url == "default.png"
json.profile_image_url "assets/small_thumb_default.png"
else
json.profile_image_url notification.sender.profile.avatar.url(:small_thumb)
end
...
end
uploader
process :resize_to_fit => [400, 400]
version :base_thumb do
process resize_to_fill: [85, 85]
end
version :small_thumb, :from_version => :base_thumb do
process :resize_to_fill => [40, 40]
end
def default_url
[version_name, "default.png"].compact.join('_')
end

Answer 1

Most likely, the file in question is inside app/assets/ folder, files inside that folder are being precompiled by default and a random digest is being added on the end of the filename. For the described behavior to work your small_thumb_default.png file should be placed inside public/ folder, so it doesn't get a digest appended on precompile. Either that or you should avoid using HTML, do it the Rails way:
# AVOID THIS
<img src="small_thumb_default.png"/>
#THIS IS PREFERABLE
<%= image_tag 'small_thumb_default.png' %>
This way you will get your view rendered with the precompiled filename.