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This article explains hHow how to block the system not to create sub-tasks if the subtasks are already existed using the Create on Transition app.

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1. Add a post-function to the intended transition to create a sub-task.
   To add a post-function, navigate to Cogwheel > Issues > Workflows > select the workflow of the project and edit the same.
2. Select Create Sub-task post function as shown below.
   
3. Select the Conditions & Configurations and add %jql_result_count% in Condition 1 and Regular expression pattern value as "0" by marking the Exact field under Conditions section.
   
   By using the %jql_result_count% and Regular expression pattern value as "0" it will check for the JQL query available under the Configuration section.
4. Under the Configuration section in the JQL query add the value as parent = %original_key%
   
   By using the parent = %original_key% in JQL query section 

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1.  which checks if the parent issue has some sub-tasks and then creates a new sub-task
2. Click Update to save the settings. Verify the condition.
   
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3. Publish the workflow draft.
4. Perform the transition In Progress as shown. You will notice that issues are created based on the condition and if the transition repeats it won't create any duplicate sub-tasks.
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