Get child, of child, of child etc

[emillykkejensen]

Postet this question on stackoverflow as well, but hoping to get better answers here.

I am trying to get all children and all parents of a doc id, where one child can be the parent, grandparent, grand grandparent etc. of multiple docs.

So let's say I have a structur like this (borrowed from https://www.elastic.co/guide/en/elasticsearch/reference/5.6/parent-join.html):

   (parent)
   question
    /    \
   /      \
comment  answer
(child)  (child)

In code:

PUT my_index
{
  "settings": {
    "mapping.single_type": true
  },
  "mappings": {
    "doc": {
      "properties": {
        "my_join_field": {
          "type": "join",
          "relations": {
            "question": ["answer", "comment"]
          }
        }
      }
    }
  }
}

However, one can answer comments and comment answers theoretically forever. So say I have a question, that is structured like this:

                               (id: 1)
                               question
                              /        \
                             /          \
                        answer          answer
                       (id: 5)          (id: 8)
                       /     \              |
                      /       \             |
                   comment  answer        answer
                  (id: 15) (id: 12)      (id: 9)
                  /    \        |          /   \  
                 /      \       |         /     \ 
              answer  answer  comment  answer  answer 
             (id: 16)(id: 17) (id: 19) (id: 10)(id: 11)

How do I get all the documents (ids 1, 5, 8, 9, 10, 11, 12, 15, 16, 17, 19), only knowing id 9?