Update Trigger Validation Example

gistfile1.txt

trigger myAccountTrigger on Account (before delete, before update) {
    if (Trigger.isBefore) {
        if (Trigger.isUpdate) {
            for (Account newAcct : Trigger.new) {
                  Account oldAcct = Trigger.oldMap.get(newAcct.Id);
                  if (oldAcct.Name != newAcct.Name &&
                      newAcct.Name.containsIgnoreCase(‘Luke’) 
                       newAcct.addError(‘Choose a better name’);
            }
        }
    }
}