How to make a field act as single select and multi-select field?

[Kay]

Hello Community!

I have a scenario that I need a single select field works as both single select and multi select. 

Example: I have two fields A & B. Field A has two options 1 & 2. When I select 1,  I want B act as a single select field. When I select 2, I want B act as a multi-select field. Is there a way to do that? B, by default, is a single select field. 

Highly appreciate all of your answer!

Kay, 

[Gustavo Félix]

Hi @Kay  , I'm not sure you can do that.

My workaround (using ScriptRunner plugin) would be to create a transition validator.
B is going to be a multiple select field.

So , if you choose "1" in A, and you selected more than one value in B, when you try to create the issue, your validator is going to check if you select more than one option.
If you did , a message is going to appear "You cant select more than one option when selecting 1". 

Something like that would work.