MattyKeene

Ruby on Rails

Programming

Cleaning Up With ActiveModel Dirty

ActiveModel::Dirty is a handy module that allows you to detect when an object has changed from the model level. I’ve found this to be incredibly helpful when you only want to run a method after a specific change occurs. You are able to track these changes by appending _changed? to the attribute being listened to.

Often times I will use ActiveModel:Dirty in a call back like so:

after_save :is_hungry

def is_hungry
  if is_hungry_changed?
    self.order_pizza
  end
end

These dirty methods also give us the ability to view what changes have been made. This can be done by appending the attribute we are expecting to change with _change, resulting in an array that contains the previous and new values.

matty.favorite_pizza = 'bbq chicken'
matty.favorete_pizza_changed? # => true
matty.favorite_pizza_change # => ['mushroom and olive', 'bbq chicken']

Another powerful option Dirty provides is the ability to return true or false when a change meets a specific requirement

matty.preferred_crust # => 'New York'
matty.preferred_crust = 'Sicilian'
matty.preferred_crust_changed?(from: 'New York', to: 'Sicilian') # => true

There are a handful of other useful methods you can read about in the Rails documentation for a deeper look into this library.

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