title: How model refers these columns?
body: <p>I am new to Ruby on Rails. I don't understand how methods written in model work. eg. </p>
  
  <pre><code>class Order &lt; ActiveRecord::Base
    has_many :line_items, dependant: :destroy
  
    def add_line_items_from_cart(cart)
      cart.line_items.each do |item|
           line_items &lt;&lt; item
      end
    end
  end
  </code></pre>
  
  <p>I don't understand how line_items are referred here. line_item is not a column of Order table then how does line_items &lt;&lt; item work.</p>
  
  <p>P.S. - This example taken from RoR book. </p>