A lookup relationship with Read/Write sharing setting is the recommended option to use when adding a field to Case Outcome custom object. A lookup relationship is a type of relationship that links two objects together and allows users to associate one record with another. A lookup relationship does not affect the security or deletion of either record and can be optional or required. In this case, you can create a lookup relationship field on Case Outcome object that references Case object and allows users to link multiple Case records to multiple Case Outcome records. You can also set the sharing setting for the lookup field to Read/Write, which means that users who have access to the parent record can also access and edit the child record. References:
https://help.salesforce.com/s/articleView?id=sf.relationships_lookup.htm&type=5 https://help.salesforce.com
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