What is the difference between Trigger.New and Trigger.NewMap?

Trigger.new and Trigger.newMap hold the same records — just in different shapes. Trigger.new is a List<SObject> (positional, ordered). Trigger.newMap is a Map<Id, SObject> (keyed by record Id, O(1) lookup). The key difference for interviews: newMap is null in before insert, because the records have no Ids yet.

Side-by-side

When to reach for which

Use Trigger.new when you’re iterating — collecting Ids, computing fields in place, walking every record once.

for (Account a : Trigger.new) {
    if (a.AnnualRevenue == null) a.AnnualRevenue = 0;
}

Use Trigger.newMap when you need lookup by Id — pairing each new record with its old version, or correlating with related records you queried separately.

trigger CaseTrigger on Case (after update) {
    Set<Id> changedIds = new Set<Id>();
    for (Case c : Trigger.new) {
        if (c.Status != Trigger.oldMap.get(c.Id).Status) changedIds.add(c.Id);
    }
    Map<Id, Case> changed = new Map<Id, Case>();
    for (Id id : changedIds) changed.put(id, Trigger.newMap.get(id));
    AuditService.logStatusChanges(changed);
}

The “construct your own map” idiom

In before insert, you don’t have Trigger.newMap, but sometimes a downstream method expects a map. You can build one from Trigger.new only after the records have Ids — i.e. in any after context:

Map<Id, Account> byId = new Map<Id, Account>(Trigger.new);

The Map<Id, SObject> constructor accepts a List<SObject> and indexes by Id automatically. This is the same data Salesforce hands you as Trigger.newMap, just constructed manually.

Common interview follow-ups

• Why is Trigger.newMap null in before insert? — Records have no Id field yet, so there’s no key to map by.
• Is Trigger.newMap available in before delete? — No, both new and newMap are null in any delete context. Use Trigger.old / Trigger.oldMap.
• Can I modify the records via Trigger.newMap? — In before contexts, yes — newMap.get(id).Field__c = value; works because it returns a reference to the same record Trigger.new holds.

Verified against: Apex Developer Guide — Trigger Context Variables. Last reviewed 2026-05-17.