Active Record Callbacks

1 The Object Life Cycle

During the normal operation of a Rails application, objects may be created, updated, and destroyed. Active Record provides hooks into this object life cycle so that you can control your application and its data.

Callbacks allow you to trigger logic before or after a change to an object's state. They are methods that get called at certain moments of an object's life cycle. With callbacks it is possible to write code that will run whenever an Active Record object is initialized, created, saved, updated, deleted, validated, or loaded from the database.

class BirthdayCake < ApplicationRecord
  after_create -> { Rails.logger.info("Congratulations, the callback has run!") }
end

irb> BirthdayCake.create
Congratulations, the callback has run!

As you will see, there are many life cycle events and multiple options to hook into these — either before, after, or even around them.

2 Callback Registration

To use the available callbacks, you need to implement and register them. Implementation can be done in a multitude of ways like using ordinary methods, blocks and procs, or defining custom callback objects using classes or modules. Let's go through each of these implementation techniques.

You can register the callbacks with a macro-style class method that calls an ordinary method for implementation.

class User < ApplicationRecord
  validates :username, :email, presence: true

  before_validation :ensure_username_has_value

  private
    def ensure_username_has_value
      if username.blank?
        self.username = email
      end
    end
end

The macro-style class methods can also receive a block. Consider using this style if the code inside your block is so short that it fits in a single line:

class User < ApplicationRecord
  validates :username, :email, presence: true

  before_validation do
    self.username = email if username.blank?
  end
end

Alternatively, you can pass a proc to the callback to be triggered.

class User < ApplicationRecord
  validates :username, :email, presence: true

  before_validation ->(user) { user.username = user.email if user.username.blank? }
end

Lastly, you can define a custom callback object, as shown below. We will cover these later in more detail.

class User < ApplicationRecord
  validates :username, :email, presence: true

  before_validation AddUsername
end

class AddUsername
  def self.before_validation(record)
    if record.username.blank?
      record.username = record.email
    end
  end
end

2.1 Registering Callbacks to Fire on Life Cycle Events

Callbacks can also be registered to only fire on certain life cycle events, this can be done using the :on option and allows complete control over when and in what context your callbacks are triggered.

class User < ApplicationRecord
  validates :username, :email, presence: true

  before_validation :ensure_username_has_value, on: :create

  # :on takes an array as well
  after_validation :set_location, on: [ :create, :update ]

  private
    def ensure_username_has_value
      if username.blank?
        self.username = email
      end
    end

    def set_location
      self.location = LocationService.query(self)
    end
end

3 Available Callbacks

Here is a list with all the available Active Record callbacks, listed in the order in which they will get called during the respective operations:

3.1 Creating an Object

• before_validation
• after_validation
• before_save
• around_save
• before_create
• around_create
• after_create
• after_save
• after_commit / after_rollback

See the after_commit / after_rollback section for examples using these two callbacks.

There are examples below that show how to use these callbacks. We've grouped them by the operation they are associated with, and lastly show how they can be used in combination.

3.1.1 Validation Callbacks

Validation callbacks are triggered whenever the record is validated directly via the valid? ( or its alias validate) or invalid? method, or indirectly via create, update, or save. They are called before and after the validation phase.

class User < ApplicationRecord
  validates :name, presence: true
  before_validation :titleize_name
  after_validation :log_errors

  private
    def titleize_name
      self.name = name.downcase.titleize if name.present?
      Rails.logger.info("Name titleized to #{name}")
    end

    def log_errors
      if errors.any?
        Rails.logger.error("Validation failed: #{errors.full_messages.join(', ')}")
      end
    end
end

irb> user = User.new(name: "", email: "john.doe@example.com", password: "abc123456")
=> #<User id: nil, email: "john.doe@example.com", created_at: nil, updated_at: nil, name: "">

irb> user.valid?
Name titleized to
Validation failed: Name can't be blank
=> false

3.1.2 Save Callbacks

Save callbacks are triggered whenever the record is persisted (i.e. "saved") to the underlying database, via the create, update, or save methods. They are called before, after, and around the object is saved.

class User < ApplicationRecord
  before_save :hash_password
  around_save :log_saving
  after_save :update_cache

  private
    def hash_password
      self.password_digest = BCrypt::Password.create(password)
      Rails.logger.info("Password hashed for user with email: #{email}")
    end

    def log_saving
      Rails.logger.info("Saving user with email: #{email}")
      yield
      Rails.logger.info("User saved with email: #{email}")
    end

    def update_cache
      Rails.cache.write(["user_data", self], attributes)
      Rails.logger.info("Update Cache")
    end
end

irb> user = User.create(name: "Jane Doe", password: "password", email: "jane.doe@example.com")

Password hashed for user with email: jane.doe@example.com
Saving user with email: jane.doe@example.com
User saved with email: jane.doe@example.com
Update Cache
=> #<User id: 1, email: "jane.doe@example.com", created_at: "2024-03-20 16:02:43.685500000 +0000", updated_at: "2024-03-20 16:02:43.685500000 +0000", name: "Jane Doe">

3.1.3 Create Callbacks

Create callbacks are triggered whenever the record is persisted (i.e. "saved") to the underlying database for the first time — in other words, when we're saving a new record, via the create or save methods. They are called before, after and around the object is created.

class User < ApplicationRecord
  before_create :set_default_role
  around_create :log_creation
  after_create :send_welcome_email

  private
    def set_default_role
      self.role = "user"
      Rails.logger.info("User role set to default: user")
    end

    def log_creation
      Rails.logger.info("Creating user with email: #{email}")
      yield
      Rails.logger.info("User created with email: #{email}")
    end

    def send_welcome_email
      UserMailer.welcome_email(self).deliver_later
      Rails.logger.info("User welcome email sent to: #{email}")
    end
end

irb> user = User.create(name: "John Doe", email: "john.doe@example.com")

User role set to default: user
Creating user with email: john.doe@example.com
User created with email: john.doe@example.com
User welcome email sent to: john.doe@example.com
=> #<User id: 10, email: "john.doe@example.com", created_at: "2024-03-20 16:19:52.405195000 +0000", updated_at: "2024-03-20 16:19:52.405195000 +0000", name: "John Doe">

3.2 Updating an Object

Update callbacks are triggered whenever an existing record is persisted (i.e. "saved") to the underlying database. They are called before, after and around the object is updated.

• before_validation
• after_validation
• before_save
• around_save
• before_update
• around_update
• after_update
• after_save
• after_commit / after_rollback

We've already covered validation and save callbacks. See the after_commit / after_rollback section for examples using these two callbacks.

3.2.1 Update Callbacks

class User < ApplicationRecord
  before_update :check_role_change
  around_update :log_updating
  after_update :send_update_email

  private
    def check_role_change
      if role_changed?
        Rails.logger.info("User role changed to #{role}")
      end
    end

    def log_updating
      Rails.logger.info("Updating user with email: #{email}")
      yield
      Rails.logger.info("User updated with email: #{email}")
    end

    def send_update_email
      UserMailer.update_email(self).deliver_later
      Rails.logger.info("Update email sent to: #{email}")
    end
end

irb> user = User.find(1)
=> #<User id: 1, email: "john.doe@example.com", created_at: "2024-03-20 16:19:52.405195000 +0000", updated_at: "2024-03-20 16:19:52.405195000 +0000", name: "John Doe", role: "user" >

irb> user.update(role: "admin")
User role changed to admin
Updating user with email: john.doe@example.com
User updated with email: john.doe@example.com
Update email sent to: john.doe@example.com

3.2.2 Using a Combination of Callbacks

Often, you will need to use a combination of callbacks to achieve the desired behavior. For example, you may want to send a confirmation email after a user is created, but only if the user is new and not being updated. When a user is updated, you may want to notify an admin if critical information is changed. In this case, you can use after_create and after_update callbacks together.

class User < ApplicationRecord
  after_create :send_confirmation_email
  after_update :notify_admin_if_critical_info_updated

  private
    def send_confirmation_email
      UserMailer.confirmation_email(self).deliver_later
      Rails.logger.info("Confirmation email sent to: #{email}")
    end

    def notify_admin_if_critical_info_updated
      if saved_change_to_email? || saved_change_to_phone_number?
        AdminMailer.user_critical_info_updated(self).deliver_later
        Rails.logger.info("Notification sent to admin about critical info update for: #{email}")
      end
    end
end

irb> user = User.create(name: "John Doe", email: "john.doe@example.com")
Confirmation email sent to: john.doe@example.com
=> #<User id: 1, email: "john.doe@example.com", ...>

irb> user.update(email: "john.doe.new@example.com")
Notification sent to admin about critical info update for: john.doe.new@example.com
=> true

3.3 Destroying an Object

Destroy callbacks are triggered whenever a record is destroyed, but ignored when a record is deleted. They are called before, after and around the object is destroyed.

• before_destroy
• around_destroy
• after_destroy
• after_commit / after_rollback

Find examples for using after_commit / after_rollback.

3.3.1 Destroy Callbacks

class User < ApplicationRecord
  before_destroy :check_admin_count
  around_destroy :log_destroy_operation
  after_destroy :notify_users

  private
    def check_admin_count
      if admin? && User.where(role: "admin").count == 1
        throw :abort
      end
      Rails.logger.info("Checked the admin count")
    end

    def log_destroy_operation
      Rails.logger.info("About to destroy user with ID #{id}")
      yield
      Rails.logger.info("User with ID #{id} destroyed successfully")
    end

    def notify_users
      UserMailer.deletion_email(self).deliver_later
      Rails.logger.info("Notification sent to other users about user deletion")
    end
end

irb> user = User.find(1)
=> #<User id: 1, email: "john.doe@example.com", created_at: "2024-03-20 16:19:52.405195000 +0000", updated_at: "2024-03-20 16:19:52.405195000 +0000", name: "John Doe", role: "admin">

irb> user.destroy
Checked the admin count
About to destroy user with ID 1
User with ID 1 destroyed successfully
Notification sent to other users about user deletion

3.4 after_initialize and after_find

Whenever an Active Record object is instantiated, either by directly using new or when a record is loaded from the database, the after_initialize callback will be called. It can be useful to avoid the need to directly override your Active Record initialize method.

When loading a record from the database the after_find callback will be called. after_find is called before after_initialize if both are defined.

They can be registered just like the other Active Record callbacks.

class User < ApplicationRecord
  after_initialize do |user|
    Rails.logger.info("You have initialized an object!")
  end

  after_find do |user|
    Rails.logger.info("You have found an object!")
  end
end

irb> User.new
You have initialized an object!
=> #<User id: nil>

irb> User.first
You have found an object!
You have initialized an object!
=> #<User id: 1>

3.5 after_touch

The after_touch callback will be called whenever an Active Record object is touched. You can read more about touch in the API docs.

class User < ApplicationRecord
  after_touch do |user|
    Rails.logger.info("You have touched an object")
  end
end

irb> user = User.create(name: "Kuldeep")
=> #<User id: 1, name: "Kuldeep", created_at: "2013-11-25 12:17:49", updated_at: "2013-11-25 12:17:49">

irb> user.touch
You have touched an object
=> true

It can be used along with belongs_to:

class Book < ApplicationRecord
  belongs_to :library, touch: true
  after_touch do
    Rails.logger.info("A Book was touched")
  end
end

class Library < ApplicationRecord
  has_many :books
  after_touch :log_when_books_or_library_touched

  private
    def log_when_books_or_library_touched
      Rails.logger.info("Book/Library was touched")
    end
end

irb> book = Book.last
=> #<Book id: 1, library_id: 1, created_at: "2013-11-25 17:04:22", updated_at: "2013-11-25 17:05:05">

irb> book.touch # triggers book.library.touch
A Book was touched
Book/Library was touched
=> true

4 Running Callbacks

The following methods trigger callbacks:

• create
• create!
• destroy
• destroy!
• destroy_all
• destroy_by
• save
• save!
• save(validate: false)
• save!(validate: false)
• toggle!
• touch
• update_attribute
• update_attribute!
• update
• update!
• valid?
• validate

Additionally, the after_find callback is triggered by the following finder methods:

• all
• first
• find
• find_by
• find_by!
• find_by_*
• find_by_*!
• find_by_sql
• last
• sole
• take

The after_initialize callback is triggered every time a new object of the class is initialized.

5 Conditional Callbacks

As with validations, we can also make the calling of a callback method conditional on the satisfaction of a given predicate. We can do this using the :if and :unless options, which can take a symbol, a Proc or an Array.

You may use the :if option when you want to specify under which conditions the callback should be called. If you want to specify the conditions under which the callback should not be called, then you may use the :unless option.

5.1 Using :if and :unless with a Symbol

You can associate the :if and :unless options with a symbol corresponding to the name of a predicate method that will get called right before the callback.

When using the :if option, the callback won't be executed if the predicate method returns false; when using the :unless option, the callback won't be executed if the predicate method returns true. This is the most common option.

class Order < ApplicationRecord
  before_save :normalize_card_number, if: :paid_with_card?
end

Using this form of registration it is also possible to register several different predicates that should be called to check if the callback should be executed. We will cover this in the Multiple Callback Conditions section.

5.2 Using :if and :unless with a Proc

It is possible to associate :if and :unless with a Proc object. This option is best suited when writing short validation methods, usually one-liners:

class Order < ApplicationRecord
  before_save :normalize_card_number,
    if: ->(order) { order.paid_with_card? }
end

Since the proc is evaluated in the context of the object, it is also possible to write this as:

class Order < ApplicationRecord
  before_save :normalize_card_number, if: -> { paid_with_card? }
end

5.3 Multiple Callback Conditions

The :if and :unless options also accept an array of procs or method names as symbols:

class Comment < ApplicationRecord
  before_save :filter_content,
    if: [:subject_to_parental_control?, :untrusted_author?]
end

You can easily include a proc in the list of conditions:

class Comment < ApplicationRecord
  before_save :filter_content,
    if: [:subject_to_parental_control?, -> { untrusted_author? }]
end

5.4 Using Both :if and :unless

Callbacks can mix both :if and :unless in the same declaration:

class Comment < ApplicationRecord
  before_save :filter_content,
    if: -> { forum.parental_control? },
    unless: -> { author.trusted? }
end

The callback only runs when all the :if conditions and none of the :unless conditions are evaluated to true.

6 Skipping Callbacks

Just as with validations, it is also possible to skip callbacks by using the following methods:

• decrement!
• decrement_counter
• delete
• delete_all
• delete_by
• increment!
• increment_counter
• insert
• insert!
• insert_all
• insert_all!
• touch_all
• update_column
• update_columns
• update_all
• update_counters
• upsert
• upsert_all

Let's consider a User model where the before_save callback logs any changes to the user's email address:

class User < ApplicationRecord
  before_save :log_email_change

  private
    def log_email_change
      if email_changed?
        Rails.logger.info("Email changed from #{email_was} to #{email}")
      end
    end
end

Now, suppose there's a scenario where you want to update the user's email address without triggering the before_save callback to log the email change. You can use the update_columns method for this purpose:

irb> user = User.find(1)
irb> user.update_columns(email: 'new_email@example.com')

The above will update the user's email address without triggering the before_save callback.

7 Suppressing Callbacks

In certain scenarios, you may need to temporarily prevent certain callbacks from being executed within your Rails application. This can be useful when you want to skip specific actions during certain operations without permanently disabling the callbacks.

Rails provides a mechanism for suppressing callbacks using the ActiveRecord::Suppressor module. By using this module, you can wrap a block of code where you want to suppress callbacks, ensuring that they are not executed during that specific operation.

Let's consider a scenario where we have a User model with a callback that sends a welcome email to new users after they sign up. However, there might be cases where we want to create a user without sending the welcome email, such as during seeding the database with test data.

class User < ApplicationRecord
  after_create :send_welcome_email

  def send_welcome_email
    puts "Welcome email sent to #{self.email}"
  end
end

In this example, the after_create callback triggers the send_welcome_email method every time a new user is created.

To create a user without sending the welcome email, we can use the ActiveRecord::Suppressor module as follows:

User.suppress do
  User.create(name: "Jane", email: "jane@example.com")
end

In the above code, the User.suppress block ensures that the send_welcome_email callback is not executed during the creation of the "Jane" user, allowing us to create the user without sending the welcome email.

8 Halting Execution

As you start registering new callbacks for your models, they will be queued for execution. This queue will include all of your model's validations, the registered callbacks, and the database operation to be executed.

The whole callback chain is wrapped in a transaction. If any callback raises an exception, the execution chain gets halted and a rollback is issued, and the error will be re-raised.

class Product < ActiveRecord::Base
  before_validation do
    raise "Price can't be negative" if total_price < 0
  end
end

Product.create # raises "Price can't be negative"

This unexpectedly breaks code that does not expect methods like create and save to raise exceptions.

class Product < ActiveRecord::Base
  before_validation do
    throw :abort if total_price < 0
  end
end

Product.create # => false

However, it will raise an ActiveRecord::RecordNotSaved when calling create!. This exception indicates that the record was not saved due to the callback's interruption.

User.create! # => raises an ActiveRecord::RecordNotSaved

When throw :abort is called in any destroy callback, destroy will return false:

class User < ActiveRecord::Base
  before_destroy do
    throw :abort if still_active?
  end
end

User.first.destroy # => false

However, it will raise an ActiveRecord::RecordNotDestroyed when calling destroy!.

User.first.destroy! # => raises an ActiveRecord::RecordNotDestroyed

9 Association Callbacks

Association callbacks are similar to normal callbacks, but they are triggered by events in the life cycle of the associated collection. There are four available association callbacks:

• before_add
• after_add
• before_remove
• after_remove

You can define association callbacks by adding options to the association.

Suppose you have an example where an author can have many books. However, before adding a book to the authors collection, you want to ensure that the author has not reached their book limit. You can do this by adding a before_add callback to check the limit.

class Author < ApplicationRecord
  has_many :books, before_add: :check_limit

  private
    def check_limit(_book)
      if books.count >= 5
        errors.add(:base, "Cannot add more than 5 books for this author")
        throw(:abort)
      end
    end
end

If a before_add callback throws :abort, the object does not get added to the collection.

At times you may want to perform multiple actions on the associated object. In this case, you can stack callbacks on a single event by passing them as an array. Additionally, Rails passes the object being added or removed to the callback for you to use.

class Author < ApplicationRecord
  has_many :books, before_add: [:check_limit, :calculate_shipping_charges]

  def check_limit(_book)
    if books.count >= 5
      errors.add(:base, "Cannot add more than 5 books for this author")
      throw(:abort)
    end
  end

  def calculate_shipping_charges(book)
    weight_in_pounds = book.weight_in_pounds || 1
    shipping_charges = weight_in_pounds * 2

    shipping_charges
  end
end

Similarly, if a before_remove callback throws :abort, the object does not get removed from the collection.

# Triggers `before_add` callback
author.books << book
author.books = [book, book2]

# Does not trigger the `before_add` callback
book.update(author_id: 1)

10 Cascading Association Callbacks

Callbacks can be performed when associated objects are changed. They work through the model associations whereby life cycle events can cascade on associations and fire callbacks.

Suppose an example where a user has many articles. A user's articles should be destroyed if the user is destroyed. Let's add an after_destroy callback to the User model by way of its association to the Article model:

class User < ApplicationRecord
  has_many :articles, dependent: :destroy
end

class Article < ApplicationRecord
  after_destroy :log_destroy_action

  def log_destroy_action
    Rails.logger.info("Article destroyed")
  end
end

irb> user = User.first
=> #<User id: 1>
irb> user.articles.create!
=> #<Article id: 1, user_id: 1>
irb> user.destroy
Article destroyed
=> #<User id: 1>

11 Transaction Callbacks

11.1 after_commit and after_rollback

Two additional callbacks are triggered by the completion of a database transaction: after_commit and after_rollback. These callbacks are very similar to the after_save callback except that they don't execute until after database changes have either been committed or rolled back. They are most useful when your Active Record models need to interact with external systems that are not part of the database transaction.

Consider a PictureFile model that needs to delete a file after the corresponding record is destroyed.

class PictureFile < ApplicationRecord
  after_destroy :delete_picture_file_from_disk

  def delete_picture_file_from_disk
    if File.exist?(filepath)
      File.delete(filepath)
    end
  end
end

If anything raises an exception after the after_destroy callback is called and the transaction rolls back, then the file will have been deleted and the model will be left in an inconsistent state. For example, suppose that picture_file_2 in the code below is not valid and the save! method raises an error.

PictureFile.transaction do
  picture_file_1.destroy
  picture_file_2.save!
end

By using the after_commit callback we can account for this case.

class PictureFile < ApplicationRecord
  after_commit :delete_picture_file_from_disk, on: :destroy

  def delete_picture_file_from_disk
    if File.exist?(filepath)
      File.delete(filepath)
    end
  end
end

When a transaction completes, the after_commit or after_rollback callbacks are called for all models created, updated, or destroyed within that transaction. However, if an exception is raised within one of these callbacks, the exception will bubble up and any remaining after_commit or after_rollback methods will not be executed.

class User < ActiveRecord::Base
  after_commit { raise "Intentional Error" }
  after_commit {
    # This won't get called because the previous after_commit raises an exception
    Rails.logger.info("This will not be logged")
  }
end

after_commit makes very different guarantees than after_save, after_update, and after_destroy. For example, if an exception occurs in an after_save the transaction will be rolled back and the data will not be persisted.

class User < ActiveRecord::Base
  after_save do
    # If this fails the user won't be saved.
    EventLog.create!(event: "user_saved")
  end
end

However, during after_commit the data was already persisted to the database, and thus any exception won't roll anything back anymore.

class User < ActiveRecord::Base
  after_commit do
    # If this fails the user was already saved.
    EventLog.create!(event: "user_saved")
  end
end

The code executed within after_commit or after_rollback callbacks is itself not enclosed within a transaction.

In the context of a single transaction, if you represent the same record in the database, there's a crucial behavior in the after_commit and after_rollback callbacks to note. These callbacks are triggered only for the first object of the specific record that changes within the transaction. Other loaded objects, despite representing the same database record, will not have their respective after_commit or after_rollback callbacks triggered.

class User < ApplicationRecord
  after_commit :log_user_saved_to_db, on: :update

  private
    def log_user_saved_to_db
      Rails.logger.info("User was saved to database")
    end
end

irb> user = User.create
irb> User.transaction { user.save; user.save }
# User was saved to database

11.2 Aliases for after_commit

Using the after_commit callback only on create, update, or delete is common. Sometimes you may also want to use a single callback for both create and update. Here are some common aliases for these operations:

• after_destroy_commit
• after_create_commit
• after_update_commit
• after_save_commit

Let's go through some examples:

Instead of using after_commit with the on option for a destroy like below:

class PictureFile < ApplicationRecord
  after_commit :delete_picture_file_from_disk, on: :destroy

  def delete_picture_file_from_disk
    if File.exist?(filepath)
      File.delete(filepath)
    end
  end
end

You can instead use the after_destroy_commit.

class PictureFile < ApplicationRecord
  after_destroy_commit :delete_picture_file_from_disk

  def delete_picture_file_from_disk
    if File.exist?(filepath)
      File.delete(filepath)
    end
  end
end

The same applies for after_create_commit and after_update_commit.

However, if you use the after_create_commit and the after_update_commit callback with the same method name, it will only allow the last callback defined to take effect, as they both internally alias to after_commit which overrides previously defined callbacks with the same method name.

class User < ApplicationRecord
  after_create_commit :log_user_saved_to_db
  after_update_commit :log_user_saved_to_db

  private
    def log_user_saved_to_db
      # This only gets called once
      Rails.logger.info("User was saved to database")
    end
end

irb> user = User.create # prints nothing

irb> user.save # updating @user
User was saved to database

In this case, it's better to use after_save_commit instead which is an alias for using the after_commit callback for both create and update:

class User < ApplicationRecord
  after_save_commit :log_user_saved_to_db

  private
    def log_user_saved_to_db
      Rails.logger.info("User was saved to database")
    end
end

irb> user = User.create # creating a User
User was saved to database

irb> user.save # updating user
User was saved to database

11.3 Transactional Callback Ordering

By default (from Rails 7.1), transaction callbacks will run in the order they are defined.

class User < ActiveRecord::Base
  after_commit { Rails.logger.info("this gets called first") }
  after_commit { Rails.logger.info("this gets called second") }
end

However, in prior versions of Rails, when defining multiple transactional after_ callbacks (after_commit, after_rollback, etc), the order in which the callbacks were run was reversed.

If for some reason you'd still like them to run in reverse, you can set the following configuration to false. The callbacks will then run in the reverse order. See the Active Record configuration options for more details.

config.active_record.run_after_transaction_callbacks_in_order_defined = false

12 Callback Objects

Sometimes the callback methods that you'll write will be useful enough to be reused by other models. Active Record makes it possible to create classes that encapsulate the callback methods, so they can be reused.

Here's an example of an after_commit callback class to deal with the cleanup of discarded files on the filesystem. This behavior may not be unique to our PictureFile model and we may want to share it, so it's a good idea to encapsulate this into a separate class. This will make testing that behavior and changing it much easier.

class FileDestroyerCallback
  def after_commit(file)
    if File.exist?(file.filepath)
      File.delete(file.filepath)
    end
  end
end

When declared inside a class, as above, the callback methods will receive the model object as a parameter. This will work on any model that uses the class like so:

class PictureFile < ApplicationRecord
  after_commit FileDestroyerCallback.new
end

Note that we needed to instantiate a new FileDestroyerCallback object, since we declared our callback as an instance method. This is particularly useful if the callbacks make use of the state of the instantiated object. Often, however, it will make more sense to declare the callbacks as class methods:

class FileDestroyerCallback
  def self.after_commit(file)
    if File.exist?(file.filepath)
      File.delete(file.filepath)
    end
  end
end

When the callback method is declared this way, it won't be necessary to instantiate a new FileDestroyerCallback object in our model.

class PictureFile < ApplicationRecord
  after_commit FileDestroyerCallback
end

You can declare as many callbacks as you want inside your callback objects.