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QUESTION: when you instantiate a class in a scheduled apex job, is the class instantiated at the time of the schedule, or at the scheduled time of execution?

Here's my situation... I have a custom object called Blast, which schedules a bulk SMS send. That object record includes a DateTime field that designates when the blast will happen; for this example, let's say the blast happens next Tuesday at 1:00 pm.

The blast has some unknown number of recipients -- very possibly 20-50k, which are stored as CampaignMembers. So, at the designated time, I have a batch apex class that retrieves all of the recipient info from the CampaignMember records and makes the api call.

When a user creates/updates the Blast record today and sets status to "queued", I'm creating a scheduled apex job, instantiating my batch apex class and providing the blast record, from which it pulls necessary data.

I want to build into the batch apex class a check that verifies the blast record still exists before executing the blast. But I'm not clear on whether that class is instantiated today (when the job is scheduled), or next Tuesday at 1:00pm when it has been scheduled to run.

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It's instantiated when new SomeBatchJobName() is called, then serialized when System.scheduleBatch(...) is called. So the data stored in the object will be from the moment of instantiation (now), not when it is eventually pulled from the queue and executed. This is also true for scheduled and queueable jobs, too.

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  • OK, thanks. That's what I thought would happen, just wanted to confirm. So that means any changes (between now and next Tuesday) to the data I use to instantiate the object will not be reflected. So... I'm thinking I need another class, that executes next Tuesday and instantiates the batch object then. – PatMcClellan__c Mar 13 '19 at 22:30
  • @PatMcClellan__c Without seeing your code, hard to say, but remember you can also do other stuff in your start method besides just providing a query locator. During the start method might be a perfect time to do any other calculations or queries you need to perform to see if you want to continue or not. You can also use System.abortJob in the start method if you want to cancel your job early (the job Id comes from the BatchableContext object). – sfdcfox Mar 13 '19 at 22:34
  • Ah... I was wondering about that. So, instead of providing the entire blast record when I instantiate, I just provide the recordId. Then, in the start method, I do a soql search on it, pull the data at that point in time, or abort if the record no longer exists. – PatMcClellan__c Mar 13 '19 at 23:01
  • @PatMcClellan__c Yes, you should always query for the data you're going to work on as late as possible, especially when using asynchronous code that might not be called for a long time. – sfdcfox Mar 13 '19 at 23:10
  • I can't find docs on how to pull the jobId while inside the start method. Would it be something like... BC.getJobId() ? – PatMcClellan__c Mar 13 '19 at 23:37
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For the benefit of clarity, I'll share my revised code... the object is actually called Wave, not Blast.

global class QueueWave implements Database.Batchable<SObject>, Database.Stateful {
global String waveId;
global String body;
global String messageServiceLabel;
global Integer recipientCount;
global String emailAddress;
global String waveName;
global String userId;

global QueueWave(String waveId) {
    this.waveId = waveId;
}

The constructor does nothing except store the recordId at the time this batch class is scheduled. I'm using try-catch, catching QueryException which aborts the job.

global Database.QueryLocator start(Database.BatchableContext BC){
    String query;
    if(Wave__c.SObjectType.getDescribe().isAccessible()){
        try{
            Wave__c wave = [
                SELECT [fields I need, which may have been updated since batch was scheduled]
                FROM Wave__c
                WHERE Id = :this.waveId
                LIMIT 1];

            //set global vars with data from the wave record
                . . .

            query = // build my query string here

        }catch(QueryException qe){
            System.debug('QueryException on ' + BC.getJobId() + ' ' + qe);
            System.abortJob(BC.getJobId());
        } 
    }  

    return Database.getQueryLocator(query);          
}

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