[twic]

Yes, this is a lot like path expressions in HQL / JPQL.

There is a key difference, i think - in JPA land, relationships between classes are named at both ends. So an OrderDetail has an "Order order" field, but an Order also has a "Set<OrderDetail> details" field. That means you already have a name to use when going from an order to its details - you can say "sum(order.details.price)". Whereas the language in the article has to make it implicit, with (IMHO weird!) syntax like "OrderDetail.sum(price)".

This starts to hurt more when you have multiple collections of the same type on an entity. Consider:

  City
    city_id
  Person
    birth_city_id
    residence_city_id

What would

  SELECT city_id, Person.COUNT()
  FROM City

do here?