How to validate custom field value from the linked issue while linking to other issue on create scn?

[Tejas Naik]

Hi,

How to validate custom field value from the linked issue while linking to other issue on create screen?

Lets just say I want to create new bug, and is having "Cause"[select type single choice] field contains "Product Feature" and "Technical Feature". 

If user select 'Cause' field as 'Product Feature' then require at least one 'Issue Link' with relationship of "Is Caused By" must exist and must have a linked GTN Epic of where the Epic's 'Feature Type' field has the value of 'Product Feature'.

Ex: Need to validate weather 'GTN-28761' has 'Feature Type' of 'Product Feature' or not while linking to other issue on create screen

I am new to groovy, can someone help me please

Thanks