Trigger Context Variables

1. 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.
2. isInsert
3. isUpdate
4. isDelete
5. 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 the API.)
6. isBefore--Returns true if this trigger was fired before any record was saved.
7. isAfter--Returns true if this trigger was fired after all records were saved
8. 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.
9. 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.
10. newMap--A map of IDs to the new versions of the sObject records.
    Note that this map is only available in after insert, and update triggers.
11. 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.
12. size--The total number of records in a trigger invocation, both old and new.
13.  Table for defining contaxt variable values "NULL" or "NOT  NULL" 

14. TCV*	Before Insert	After Insert	Before Update	After Update	Before Delete	After Delete	After Undelete
    New	NOT NULL, MODIFIABLE	NOT NULL	NOT NULL	NOT NULL	NULL	NULL	NOT NULL
    Old	NULL	NULL	NOT NULL	NOT NULL	NOT NULL	NOT NULL	NULL
    newMap	NULL	NOT NULL	NOT NULL	NOT NULL	NULL	NULL	NOT NULL
    oldMap	NULL	NULL	NOT NULL	NOT NULL	NOT NULL	NOT NULL	NULL

*TCV->Trigger Context Variable

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