What is purpose of around_create callback in Rails Model?

Question

when is around_create callback code executed, in what situations we should use it?

Answer 1

Had this question, too, and have now found the answer: around_create allows you to basically do both a before_create and an after_create in one method. You have to use yield to execute the save in between.

class MyModel < ActiveRecord::Base
  around_create :my_callback_method

  private
    def my_call_back_method
      # do some "before_create" stuff here

      yield  # this makes the save happen

      # do some "after_create" stuff here
    end
end

Answer 2

Just found one use case for me:

Imagine a situation with polymorphic watcher and the watcher in some cases needs to perform action before save and in other cases after it.

With around filter you can capture save action in a block and run it when you need.

class SomeClass < ActiveRecord::Base

end

class SomeClassObserver < ActiveRecord::Observer
  def around_create(instance, &block)
    Watcher.perform_action(instance, &block)
  end
end

# polymorphic watcher
class Watcher
  def perform_action(some_class, &block)
    if condition?
      Watcher::First.perform_action(some_class, &block)
    else
      Watcher::Second.perform_action(some_class, &block)
    end
  end
end

class Watcher::First
  def perform_action(some_class, &block)
    # update attributes
    some_class.field = "new value"

    # save
    block.call
  end
end

class Watcher::Second
  def perform_action(some_class, &block)
    # save
    block.call

    # Do some stuff with id
    Mailer.delay.email( some_class.id )
  end
end