require subfield_A if subfield_B is filled

I have a field group named cb_dog3, which includes the subfields cb_dogname and cb_rabiesexpire. In an auto action, I'm using the condition [cb:userdata field="_cb_dog3_0_cb_dogname" /] is not empty and  [cb:userdata field="_cb_dog3_0_cb_rabiesexpire" /] is empty, I want to make the rabiesexpire subfield required and return an error message. Have I set the condition up correctly? Is there a PHP code (or other way) that will do this?

The substitution format is as follows.

[FIELDGROUP_ROW_FIELDNAME]

Field Group = cb_myfields
First Row = 0
Field = cb_favoritecolor

This would give a substitution of the following.

[cb_myfields_0_cb_favoritecolor]

It's generally not ideal accessing the nested fields though. You'd have to know the exact row number and there's not a guarantee that row would always exist. Ideally you'd use PHP and access them via the JSON. Example as follows using the above.



You can use PHP to loop through the Registry object for more control.