How do you solve N+1 for ActiveStorage URLs?

Question

How do you preload all the records with their URLs?

This is what I am doing in my jbuilder to get the URLs:

# views/users/index.json.jbuilder
...
json.avatar_url user.avatar.attached? && rails_blob_url(user.avatar)
...


Comment
    has_one :user

User
    has_one_attached :avatar

How would you preload all the users and their avatars?

---

Comments.includes(users: :avatar)

yields the following error:

ActiveRecord::AssociationNotFoundError (Association named 'avatar' was not found on User; perhaps you misspelled it?)

The same error pops up when executing:

User.includes(:avatar)

Answer 1

For a singular attachment named :avatar, Active Storage adds a with_attached_avatar scope that preloads the relevant associations:

@users.with_attached_avatar.each do |user|
  # ...
end

See the API documentation for has_one_attached.