Trigger Context Variables

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 the API.)
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.
Note
If any record that fires a trigger includes an invalid field value (for example, a formula that divides by zero), that value is set to null in the new, newMap, old, and oldMap trigger context variables.

For example, in this simple trigger, Trigger.new is a list of sObjects and can be iterated over in a for loop, or used as a bind variable in the IN clause of a SOQL query:

Trigger t on Account (after insert) {
    for (Account a : Trigger.new) {
        // Iterate over each sObject
    }

    // This single query finds every contact that is associated with any of the
    // triggering accounts. Note that although Trigger.new is a collection of
    // records, when used as a bind variable in a SOQL query, Apex automatically
    // transforms the list of records into a list of corresponding Ids. Contact[] cons = [SELECT LastName FROM Contact WHERE AccountId IN :Trigger.new]; }

This trigger uses Boolean context variables like Trigger.isBefore and Trigger.isDelete to define code that only executes for specific trigger conditions:

trigger myAccountTrigger on Account(before delete, before insert, before update, 
                                    after delete, after insert, after update) {
if (Trigger.isBefore) {
    if (Trigger.isDelete) {

        // In a before delete trigger, the trigger accesses the records that will be
        // deleted with the Trigger.old list.
        for (Account a : Trigger.old) { if (a.name != 'okToDelete') { a.addError('You can\'t delete this record!'); } } } else { // In before insert or before update triggers, the trigger accesses the new records
    // with the Trigger.new list.
        for (Account a : Trigger.new) { if (a.name == 'bad') { a.name.addError('Bad name'); } } if (Trigger.isInsert) { for (Account a : Trigger.new) { System.assertEquals('xxx', a.accountNumber); System.assertEquals('industry', a.industry); System.assertEquals(100, a.numberofemployees); System.assertEquals(100.0, a.annualrevenue); a.accountNumber = 'yyy'; } // If the trigger is not a before trigger, it must be an after trigger. } else { if (Trigger.isInsert) { List<Contact> contacts = new List<Contact>(); for (Account a : Trigger.new) { if(a.Name == 'makeContact') { contacts.add(new Contact (LastName = a.Name, AccountId = a.Id)); } } insert contacts; } } }}}
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