title: DDD: Aggregates and sub-aggregates
body: <p>I have a quite complex aggregate, with aggregate root <code>Order</code>. It contains entities (eg. <code>OrderItem</code>) which are meaningless outside an aggregate. But there are also entities that are supposed to be part of this aggregate, but also do make sense outside this aggregate (eg. <code>ShippingMethod</code> or <code>Invoice</code>).</p>
  
  <p>Is it right to have a repository for this complex aggregate (loading whole aggregate by root's id) and also have CRUD repository for managing possible shipping methods and another repository for listing invoices?</p>
  
  <p>More generally, is it possible in DDD to have an aggregate, which is part of another aggregate?</p>