Rails order by association field

Merge can make the query smaller/saner-looking, and it benchmarked faster for me in Rails 4.x:

@users = User.joins(:user_extension).merge(UserExtension.order(company: :desc))

Try this:

@users = User.includes(:user_extension).order("user_extensions.company desc")

I think you need at order: user_extensions, not user_extension