Context Variable Considerations
Be aware of the following considerations for trigger context variables:
- trigger.new and trigger.old cannot be used in Apex DML operations.
- You can use an object to change its own field values using trigger.new, but only in before triggers. In all after triggers, trigger.new is not saved, so a runtime exception is thrown.
- trigger.old is always read-only.
- You cannot delete trigger.new.
The following table lists considerations about certain actions in different trigger events: