WhoId and WhatId are both "polymorphic" fields, meaning they can be related to different objects, defined by the ID itself. We can relate WhatId on a Task record to a different custom object by checking "Allow Activities" checkbox on the custom object settings page. But what about WhoId?

Currently I see that WhoId is associated with either contacts or leads. How can we associate WhoId with another custom object? And is this really possible?

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1 Answer 1


This can't be done

WhoId can only be Lead, Contact

The WhoId represents a human such as a lead or a contact. WhoIds are polymorphic. Polymorphic means a WhoId is equivalent to a contact’s ID or a lead’s ID. The label is Name ID.

This is a polymorphic relationship field.

Relationship Name


Relationship Type


Refers To

Contact, Lead

WhatId can be any custom object plus a bunch of standard objects like Opportunity

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