After_Commit for an Attribute

Checking if an attribute changed after commit in Rails

I do not know if there is any better way, but I would do:

if @item.previous_changes.has_key?('name')
  # Name has been changed.
end

Rails, using the dirty or changed? flag with after_commit

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.

Rails after commit condition

Got it. Called another callback before_update and self.status_changed? value is stored in a flag as @flag = self.status_changed?
Thanks to this article - http://axonflux.com/offlining-denormalized-tasks-gotchas-with-off.

Also cheers to Dave Newton for the kind help.

Prevent infinite loop when updating attributes within after_commit, :on = :create

You can use the method update_column that will skip all callbacks of your model:

self.update_column(:filename, filename)

Or you could use the method update_all, wich follows the same behavior

self.class.where('id = ?', self.id).update_all(:filename => filename)

And last but not least, my personal favorite:

self.filename = filename
self.send(:update_without_callbacks)

This one makes it pretty clear that all callbacks are been ignored, what is very helpful

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Also, as a different alternative, you coud use after_create instead of after_commit if you want to run the generate method only when a new record is saved

Tracking model changes in after_commit :on = :create callback

You can't use the rails changed? method, as it will always return false. To track changes after the transaction is committed, use the previous_changes method. It will return a hash with attribute name as key. You can can then check if your attribute_name is in the hash:

after_commit :foo

def foo
 if previous_changes[attribute_name]
   #do your task
 end
end

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