Automation or Rule to not allow assignee to be request participants

[Jeremy Price]

I am seeing if there is a way to block users from being an assignee and a request participant on the same ticket?

ex. After a ticket is created and already assigned to "JSmith", another participant or reporter or users in Jira shouldn't be able to add "JSmith" as a request participant also. 

Any automation or feature I can possibly use to prevent this particular action? 

[Alexey Matveev · Accepted solution]

Hello,

You can use either the Power Scripts or ScriptRunner plugin to develop such a validator.

[Jeremy Price]

Ok, only writing a script would allow me to do this it seems. I do have JWME that allows me to write in Groovy (which I'm not proficient at) , so I'm assuming that would work if I have the right code written? 

[Alexey Matveev]

Yes, JWME also would work