Add Ensure Record Saved With after_commit Callback as a Rails TIL

rails/ensure-record-saved-with-after-commit-callback.md

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+# Ensure Record Saved With after_commit Callback
+
+In my experience, some of the more common `ActiveRecord` callbacks are ones
+like `before_save` or `after_update`. While working with some code, where I
+needed to send a notification when a certain value was updated, I learned that
+something like `after_update` wasn't sufficient.
+
+If my record is updated within a transaction, the `after_update` will get
+triggered even though the changes could later get rolled back resulting in me
+erroneously sending the notification.
+
+```ruby
+ActiveRecord::Base.transaction do
+  user.update(interesting_value: 123)
+
+  do_something # <-- rollback could happen here!
+end
+```
+
+To ensure I'm not over-eager with my notifications, I should instead use
+[`after_commit`](https://api.rubyonrails.org/v7.0.5/classes/ActiveRecord/Transactions/ClassMethods.html#method-i-after_commit)
+which only gets called after the changes have been committed to the database.
+
+```ruby
+class User < ApplicationRecord
+  after_commit :send_notification,
+    on: [:create, :update],
+    if: :interesting_value_was_changed?
+
+  # rest of class...
+
+  private
+
+  def send_notification
+    # logic...
+  end
+
+  def interesting_value_was_changed?
+    # logic...
+  end
+end
+```
+
+On either `create` or `update` if my condition is met, then after the _commit_
+goes through, the `#send_notification` method will be triggered.