title: Create related objects after initialize another object in rails
body: <p>I have the below models:</p>
  
  <pre><code>class Foo &lt; ActiveRecord::Base
      has_many :bars
  end
  
  class Bar &lt; ActiveRecord::Base
      belongs_to :foo
  end
  </code></pre>
  
  <p>In the business logic, when initializing an object <code>foo</code> <code>f = Foo.new</code> three bars need to be initialized, too.
  How can I do this?</p>