Rails ActiveRecord条件回调问题

Question

ruby 2.1.8 rails 3.2.18

I am trying to run a callback when a record is saved only if a particular attribute has been changed. For example

before_save :do_the_thing, if: :my_attr_changed?

However, when I change my_attr and save, do_the_thing is not getting called. And yet, if I do the exact same thing, but with:

before_save :do_the_thing

def do_the_thing
  puts my_attr_changed?
end

It outputs "true" into the logs. Rather confused here. Any help appreciated. Thanks.

Answer 1

把它移到lambda里面吧

before_save :do_the_thing, if: -> { my_attr_changed? }