In sales orders I have 2 custom fields Qnty and Free Qnty and a checkbox Free Qnty Only. For orders, that have a number in Quantity it's possible to enter Free Quantity and the checkbox is set to false by default.
But if the checkbox Free Qnty Only is true, the Free Qnty should be uneditable. I know, that the field dependency can be set only between checkboxes and picklists, but maybe a validation rule would work here? Or is it only doable with an apex class?