How to mention parent child relation in logstash

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

You can't unfortunately.

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}"