override nested attributes in rails

Question

what happens when I override nested attributes method in rails. For example,

class Order
  has_many :line_items
  accepts_nested_attributes_for :line_items

  def line_item_attributes=(attr)
   # what can I do here.
  end
end

class LineItem
  belongs_to :order
end

In the above code ,

1. Inside line_item_attributes= method, can I add/modify/delete line items of the order?
2. When is line_items_attributes= invoked, if I call @order.save(params) ?

Answer 1

Use an alias

In Rails 4, you can override and call super.

In earlier versions, you can use Ruby's alias:

class Order
  has_many :line_items
  accepts_nested_attributes_for :line_items

  # order of arguments is new_name, existing_name
  alias :original_line_items_attributes= :line_items_attributes=
  def line_items_attributes=(attrs)
   modified_attributes                 = my_modification_method(attrs)
   self.original_line_items_attributes = modified_attributes
  end

end