A callback is a method that gets called at specific moments of an object's lifecycle (right before or after creation, deletion, update, validation, saving or loading from the database).

For instance, say you have a listing that expires within 30 days of creation.

One way to do that is like this:

class Listing < ApplicationRecord
  after_create :set_expiry_date

  private

  def set_expiry_date
    expiry_date = Date.today + 30.days
    self.update_column(:expires_on, expiry_date)
  end
end

All of the available methods for callbacks are as follows, in the same order that they are called during the operation of each object:

Creating an Object

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

Updating an Object

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

Destroying an Object

• before_destroy
• around_destroy
• after_destroy
• after_commit/after_rollback

*NOTE: after_save runs both on create and update, but always after the more specific callbacks after_create and after_update, no matter the order in which the macro calls were executed.*