Add Ensure Record Saved With after_commit Callback as a Rails TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1316 TILs and counting..._
+_1317 TILs and counting..._
 
 ---
 
@@ -807,6 +807,7 @@ _1316 TILs and counting..._
 - [Disambiguate Where In A Joined Relation](rails/disambiguate-where-in-a-joined-relation.md)
 - [Ensure A Rake Task Cannot Write Data](rails/ensure-a-rake-task-cannot-write-data.md)
 - [Ensure Migrations Use The Latest Schema](rails/ensure-migrations-use-the-latest-schema.md)
+- [Ensure Record Saved With after_commit Callback](rails/ensure-record-saved-with-after-commit-callback.md)
 - [Find Or Create A Record With FactoryBot](rails/find-or-create-a-record-with-factory-bot.md)
 - [Find Records With Multiple Associated Records](rails/find-records-with-multiple-associated-records.md)
 - [Force All Users To Sign Out](rails/force-all-users-to-sign-out.md)

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

@@ -0,0 +1,45 @@
+# 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.