Trigger Context Variables

What Is Trigger Context Variables?

Context Variables allow developers to access the run-time context of any trigger.

These context variables are contained in system.trigger class.

Considerations Of Context Variables

Points to consider with Trigger Context Variables:

1. Trigger.new and Trigger.old cannot be used in Apex DML Operations.
2. You can use an sObject to change its own field values using a trigger.new but only in before triggers.
3. Trigger.old is always read-only.
4. You can not delete Trigger.new.
5. Upsert and merge events do not have their own triggers, instead, they fire other triggers based on the events as a result of the merge operation.

Types of Trigger Context Variables

1. Trigger.new:  This variable returns a list of the new version of sObject records.
2. Trigger.old: This variable returns a list of the old version of sObject records.
3. Trigger.newMap: This variable returns a map of ids to the new versions of sObject records.
4. Trigger.oldMap:  A map of IDs to the old version of the sObject records.