While a nested query can always return only the root document as a result, parent and child documents are independent and each can be queried independently. The has_child query allows us to return parents based on data in their children, and the has_parent query returns children based on data in their parents.nested query는 결과로 root document만 반환하지만, 부모와 자식 document는 독립적이며, 각각 독립적으로 query될 수 있다. h..