rails: association callbacks

association_callbacks_md

# Association Callbacks

Normal callbacks hook into the life cycle of Active Record objects, allowing you to work with those objects at various points. For example, you can use a :before_save callback to cause something to happen just before an object is saved.

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

## avaliable callbacks

- before_add
- after_add
- before_remove
- after_remove

```
class Customer < ActiveRecord::Base
  has_many :orders, before_add: :check_credit_limit
 
  def check_credit_limit(order)
    ...
  end
end
```

```
class Customer < ActiveRecord::Base
  has_many :orders,
    before_add: [:check_credit_limit, :calculate_shipping_charges]
 
  def check_credit_limit(order)
    ...
  end
 
  def calculate_shipping_charges(order)
    ...
  end
end
```