Asynchronous Apex Triggers - Summer ‘19

Asynchronous Apex triggers are change event triggers that run asynchronously after a database transaction is completed. They are ‘after-insert’ triggers and can be defined with the after insert keywords. They can be created the same way you create regular Apex triggers. You set the trigger to use a change event object instead of an sObject. The change event object name is suffixed with ChangeEvent. For example, Account change event object is named AccountChangeEvent. The change event object name for the custom object is suffixed with __ChangeEvent.

How does it work?

When a record is created or updated, Change Data Capture publishes an event and a change event trigger can then process that event asynchronously.

Let’s look at an example transaction. Whenever an opportunity record is created or updated, you need to check whether the corresponding account is qualified to be a high priority customer. This process of qualifying high priority customers is very limit-intensive and computationally slow.

For this scenario, we can enable Change Data Capture for the Opportunity object, then implement the complex business logic in the OpportunityChangeAsyncTrigger (asynchronous Apex trigger).

When the opportunity record is created or changed, the OpportunityChangeAsyncTrigger is automatically fired and executes the complex business logic defined in AccountClassifier. Each change event processed in the trigger contains the changed record fields and metadata information about the change in header fields.

Pictorial representation of transactional flow for the example transaction]

Let’s write the code by using the CLI from the VS Code terminal. You can create the asynchronous trigger by using the following command. You can then write the code with in this trigger block and push it to your org.

sfdx force:apex:trigger:create -n OpportunityChangeAsyncTrigger -s OpportunityChangeEvent -e 'after insert' -d 'force-app/main/default/triggers'

In this code, Trigger.new() contains list of change events after the database operation. In the for loop, we are extracting the Opportunity ID, which is processed to identify the high priority Account. The classifyAccountmethod of AccountClassifier class is very limit-intensive and computationally slow, hence we are calling it outside the transaction in this asynchronous trigger. You can also create this trigger from the Developer Console by selecting File→New→ Apex Trigger and then OpportunityChangeEvent for the sObject.

trigger OpportunityChangeAsyncTrigger on OpportunityChangeEvent (after insert) {
    List<OpportunityChangeEvent> changes = Trigger.new;
    
    Set<String> oppIds = new Set<String>();
    
    //Get all record Ids for this change and add it to a set for further processing
    for(OpportunityChangeEvent opp: changes){
        List<String> recordIds = opp.ChangeEventHeader.getRecordIds();
        oppIds.addAll(recordIds);
    }
    
    
    //Perform heavy computation operation which may take a lot of time
    AccountClassifier classifier = new AccountClassifier();
    Map<String, String> highPriorityAccounts = classifier.classifyAccount(new List<String>(oppIds));
}