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:
| Trigger Event | Can change fields using trigger.new | Can update original object using an update DML operation | Can delete original object using a delete DML operation |
|---|
before insert | Allowed. | Not applicable. The original object has not been created; nothing can reference it, so nothing can update it. | Not applicable. The original object has not been created; nothing can reference it, so nothing can update it. |
after insert | Not allowed. A runtime error is thrown, as trigger.new is already saved. | Allowed. | Allowed, but unnecessary. The object is deleted immediately after being inserted. |
before update | Allowed. | Not allowed. A runtime error is thrown. | Not allowed. A runtime error is thrown. |
after update | Not allowed. A runtime error is thrown, as trigger.new is already saved. | Allowed. Even though bad code could cause an infinite recursion doing this incorrectly, the error would be found by the governor limits. | Allowed. The updates are saved before the object is deleted, so if the object is undeleted, the updates become visible. |
before delete | Not allowed. A runtime error is thrown. trigger.new is not available in before delete triggers. | Allowed. The updates are saved before the object is deleted, so if the object is undeleted, the updates become visible. | Not allowed. A runtime error is thrown. The deletion is already in progress. |
after delete | Not allowed. A runtime error is thrown. trigger.new is not available in after delete triggers. | Not applicable. The object has already been deleted. | Not applicable. The object has already been deleted. |
after undelete | Not allowed. A runtime error is thrown. | Allowed. | Allowed, but unnecessary. The object is deleted immediately after being inserted. |
