I can't catch the changed attributes on after_save callback but I can catch them on after_update callback. I think after_save is just a combination of after_create and after_update. I'd appreciate it if someone give me at least a hint.
class Student < ApplicationRecord
after_save: after_save_callback
def after_save_callback
if username_changed? ### This is always false
# do something
end
end
end
student = Student.create(name: 'John Doe', username: 'abcdef')
student.username = '123456'
student.save
My Rails version is 5.0.7.