How do I map custom fields as relational?

[Samuel Wilkinson]

I am sinking external data to a custom field. How can I somehow map that to either another custom field or a standard user field like assignee? My external data has the association between custom field value A and user 1. I just can't find a way to make this connection in jira without making a whole bunch of automation rules.

[jira guy]

Assignee is a user picker, you can't really populate data to this field. 

By default, JIRA doesn't let you add like attributes(custom field) to the user field. You should look into third party plugins. 

[Samuel Wilkinson]

I'm open to add-ons, but I have yet to find one that achieves my goal. Really any system that can match two fields based off some kind of association would help. ex if Field A option 1 is selected, Field B should be option 3