Formula to relete emails with entity

[Enju]

Hello,
In Opportunity i Have stage "Convert to Case". I create workflow which create releted Case to this Opportunity, but I don't know how to relate the same emails from the Opportunity to the created Case.

$ids = ??? (some sugestions)
entity\addLinkMultipleId('emails', $ids) 

Thanks for any help.

[Maximus]

Hello,
Email entity has the default parent relationship which supports only connections for example from one email to one opportunity. So if you will use this connection to link a new Case to the desired email, you will lose your existed link between Email and Opportunity.
To make it work you can try to create a new relationship (One-to-One) between Case and Email and use Formula to link Email with the new Case.