Is there a way to set a checkbox as true only for records corresponding with certain conditions. I have the Assignment custom object, and on that I have the "Is Default" checkbox, a role picklist field and a contact lookup field. I would like the "Is Default" checkbox to be checked only on one record that contains the same contact, and to not allow you to set it on two or more records with the same contact. But it should also allow for someone to change the record that contains the checkbox (in case it was placed by mistake). Is there any way to do that without dev?