How to make a DML operation in a trigger After insert/update (Recursion Trigger)

Many times I’ve faced requirements to write a field in a trigger after the record is inserted or update. So, naturally I’ve tried something like this:

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trigger changeValueAfter on Account (after insert) {       for (Account a: Trigger.new) {                   a.Name =  a.Id + 'Value forced to be set after by an extrange req';     }     }

But there the record is read only and if you try to change a field value this exception will be fired:

execution of AfterInsert caused by: System.FinalException: Record is read-only

The workaround is quite simple. The object contained by the global trigger.new is read-only, but you can create a new object referring the same ID and change the value that you need.

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trigger changeValueAfter on Account (after insert) {       //list of new instance of object to update.     Account[] accounts = new Account[]{};        for (Account a: Trigger.new) {        //here the magic by creating a new instance using the same id         Account aux  = new Account(Id = a.Id);               aux.Name =  a.Id + 'Value forced to be set after by an extrange req';         accounts.add(aux);     }         //then update the new instance list.     update accounts; }

In addition you have to avoid the recursion since you are changing the record the trigger will be fired again. To avoid that you have to use a static flag which says that the trigger has been already executed during the current executing context.

So, the final code should be like this:

Java

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trigger changeValueAfter on Account (after insert) {   TriggerHelper.updateValues();      }     public class TriggerHelper {   public static boolean isExecuting = false;   public static void updateValues(){   if( TriggerHelper.isExecuting ){ // if was executed during the same context // avoid recursion return; }   TriggerHelper.isExecuting = true; //list of new instance of object to update.     Account[] accounts = new Account[]{};        for (Account a: Trigger.new) {        //here the magic by creating a new instance using the same id         Account aux  = new Account(Id = a.Id);               aux.Name =  a.Id + 'Value forced to be set after by an extrange req';                 accounts.add(aux);     }         //then update the new instance list.     update accounts;   }   }