Validation rule to make WhoId required on Task

Question

I am trying to write validation rule on task to make WhoId as required field. Tried following as Error Condition formula :

ISBLANK(WhoId)
ISNULL((WhoId)

After little research found that WhoId is a polymorphic field and this field cannot be used in salesforce validation rule formula.

Are there any workarounds for this or am I missing anything here? (I want to avoid writing code for this unless it is the last option)

Answer 1

You appear to have an extra opening parenthesis. This Validation Rule saves for me:

ISBLANK(WhoId)

Whereas the formula you provided gives a syntax error:

Error: Syntax error. Missing ')'

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Here are some screenshots to prove it works in my org:

Rule

Error

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PS - A word on the post you refer to from which you interpreted you cannot reference WhoId. You cannot reach through that relationship to get fields off the Who parent, but you can reference the WhoId field itself.

No Joy

Who.Name

Joy

WhoId