Schedule a Queueable class

Question

i am quite new to salesforce so i am not sure about this, and i wanted to get a clear answer since i haven't found one yet. Can i schedule a Queueable class that basically makes a callout to get and insert Accounts, and then queues another callout to get and insert Contacts? Something like:

global class scheduledClass implements Schedulable {
   global void execute(SchedulableContext SC) {
      System.enqueueJob(new QueueExample());
   }
}

I need to schedule that to run every 4 hours.

Answer 1

You can do this. Here are some of the things to keep in mind.

1. To run every 4 hours, schedule your scheduled job using Cron expression [0]

2. If you want to your queueable to make callout, make sure you implement Database.AllowsCallouts [1]

3. In Apex code (be it Queueable, Batch job) once your make changes to db, you cannot make callouts. So make sure you adjust your code accordingly (either to separate into different jobs or do all callouts and then make db changes) [2]

4. Scheduled job can start 20 other queueable jobs and one queueable job can start one other queueable job. This allows you to chain your jobs. [1]

[0] https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_scheduler.htm

[1] https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_queueing_jobs.htm

[2] You have uncommitted work pending. Please commit or rollback before calling out error