Be aware of the following considerations for trigger context variables:
1) trigger.new and trigger.old cannot be
used in Apex DML operations.
2) 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.
3) trigger.old is always read-only.
4) 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.
|
|
|
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. trigger.old is not
available in after undelete triggers.
|
Allowed.
|
Allowed, but unnecessary. The object is deleted immediately after
being inserted.
|
All triggers define implicit
variables that allow developers to access runtime context. These variables are
contained in the System.Trigger class:
|
Variable
|
Usage
|
|
isExecuting
|
Returns true if the current context for the Apex code is a
trigger, not a Visualforce page, a Web service, or
an executeanonymous() API call.
|
|
isInsert
|
Returns true if this trigger was fired due to an insert operation,
from the Salesforce user interface, Apex, or the API.
|
|
isUpdate
|
Returns true if this trigger was fired due to an update operation,
from the Salesforce user interface, Apex, or the API.
|
|
isDelete
|
Returns true if this trigger was fired due to a delete operation, from
the Salesforce user interface, Apex, or the API.
|
|
isBefore
|
Returns true if this trigger was fired before any record was saved.
|
|
isAfter
|
Returns true if this trigger was fired after all records were saved.
|
|
isUndelete
|
Returns true if this trigger was fired after a record is recovered
from the Recycle Bin (that is, after an undelete operation from
the Salesforce user interface, Apex, or theAPI.)
|
|
new
|
Returns a list of the new versions of the sObject records.
Note that this sObject list is only available
in insert and update triggers, and the records can only
be modified in before triggers.
|
|
newMap
|
A map of IDs to the new versions of the sObject records.
Note that this map is only available
in before update, after insert,
and after update triggers.
|
|
old
|
Returns a list of the old versions of the sObject records.
Note that this sObject list is only available
in update and delete triggers.
|
|
oldMap
|
A map of IDs to the old versions of the sObject records.
Note that this map is only available
in update and delete triggers.
|
|
size
|
The total number of records in a trigger invocation, both old and new.
|
