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?

Putrescine

Answer 1

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.

Overlay

Right, sorry, missed that part of it. After saving the model the changed attributes are wiped out, so this would be pretty useless... Could you yourself store the changed attributes using before_save, for instance, and then retrieve them afterwards? – Overlay

changed?/changes will work in after_save, but not after_commit. Instead, you can use previous_changes in after_commit- see @Jonathan's answer – Allopathy

Answer 2

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

Zorina

activerecord is cool, I just had one example of previous_changes - t.co/yjCLEdDHYH – Enfold

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

Abeyant