Rails, using the dirty or changed? flag with after_commit

Question

I heard rails has a dirty/change flag. Is it possible to use that in the after_commit callback?

In my user model I have:

after_commit :push_changes

In def push_changes I would like a way to know if the name field changed. Is that possible?

Answer 1

You can use previous_changes in after_commit to access a model's attribute values from before it was saved.

see this post for more info: after_commit for an attribute

Answer 2

You can do a few things to check...

First and foremost, you can check an individual attribute as such:

user = User.find(1)
user.name_changed? # => false
user.name = "Bob"
user.name_changed? # => true

But, you can also check which attributes have changed in the entire model:

user = User.find(1)
user.changed     # => []
user.name = "Bob"
user.age = 42
user.changed     # => ['name', 'age']

There's a few more things you can do too - check out http://api.rubyonrails.org/classes/ActiveModel/Dirty.html for details.

Edit:

But, given that this is happening in an after_commit callback, the model has already been saved, meaning knowledge of the changes that occurred before the save are lost. You could try using the before_save callback to pick out the changes yourself, store them somewhere, then access them again when using after_commit.

Answer 3

Since Rails 5.1, in after_commit you should use saved_change_to_attribute?

Ref: Rails 5.1.1 deprecation warning changed_attributes