How to mention parent child relation in logstash

Elastic Stack Logstash
1

We can create parent child relation in the mapping document. How to do it in the logstash. Please help on this

2

You can't unfortunately.

3

We have to create the parent child index in elastic search. Once it created we can load the data from logstash.
In logstash we add the element parent => "%{parentdocument index id}". No specific change in the parent document logstash config

output {
elasticsearch {
index => "indexName"
document_id => "%{document id}"
document_type => "document type"
parent => "%{parent document id}"
}
}