How to create sub-task when the parent issue is not having any

Overview

This article explains how to create a sub-task using the app Create on Transition - Create Sub-task post function, when one does not already exist for the respective parent issue.

Instructions

You need to add a post function in the workflow associated with the parent issue. To create a post function:

1. Log into Jira as an Administrator and click  > Issues.
2. Under the Workflows section, select the intended workflow and click the Edit link.
3. Select the transition to which you wish to add the post-function. Select the Post Function option as the following:
   
4. Click the Add Post Function link and select Create Sub-task from the available options.
5. Once you add all the required fields to the post function, you see that the post function is added to the post functions list as the following:
   
6. Click Update and publish the workflow.

Once the post function is created for the required transition, you notice that a sub-task is created for the issue after transitioning to the selected state.