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Validation rule: Enabling Field Dependency

I’m trying to use a validation rule to make a field required depending on the value of another field.


I have 2 fields

  • FieldA – (Type = Checkbox)
  • FieldB – (Type = Text 255 chars)


If FieldA is set (ie the checkbox is checked), I want to make FieldB mandatory.  I created the following validation rule which would evaluate to TRUE and subsequently show an error message on Field B:


AND(FieldA <> null, ISBLANK(FieldB))


Unfortunately this does not work.  When I check the checkbox for FieldA and leave FieldB blank, I get no error message - What am I doing wrong? 


Also, the ISBLANK(expression) does not seem to work on fields that are of type Checkbox, so I had changed my expression.


Any ideas?  This seems to be pretty basic

Best Answer chosen by Admin (Salesforce Developers) 

Since FieldA is a checkbox, which stores boolean values, the validation rule should stick to only two possible values when comparing. i.e true or false. Hence the following will help



             FieldA = true,