Using parent-child documents, we can easily find answers to questions and similarly, to questions that have a specific answer. Let's see how we can design such a schema in this section.

Imagine we have a forum like stackoverflow, where users can ask questions. Let's assume we are setting up such a schema in an index called "post".

First, let's create the index "post":

curl -XPOST localhost:9200/posts 

We created a posts index to which we index the posts by users. Now, let's give our Elasticsearch instance an insight of what we will do by defining the mapping:

curl -XPOST localhost:9200/posts/rating/_mapping -d '{
  "rating":{
    "_parent": {"type": "post"}
  }
}'

As explained earlier, here we are mapping the type "post" as the parent of the type "rating".

Now, let's index our parent and child documents:

// Already indexed

With this, we have set up the schema design to store questions and answers.

Now, let's look into a requirement. It's required for a...