Issue with Schedulable implementation and Callout

Question

I am receiving an error message when trying to test a class that implements Schedulable.

System.CalloutException: Callout from scheduled Apex not supported.

People have suggested using the @future method, but I am worried about my application being out of sync. I am using a callout to synchronize a Salesforce object to another system and then update the Salesforce object with the ID from the other system. My though is that the @future method may prevent that from happening in a linear fashion (SOQL to get sObject, Callout to create and get the ID from other system, Update sObject with ID).

I have looked at using a Database.Batchable interface but am a bit lost. All I need the batch to do is the following.

bigClass sync = new bigClass();
sync.init();

Batchable's execute method appears to require a List. Is there any way to have it just run the init method?

Answer 1

I'm pretty sure that this will work (assuming that you don't need to schedule back to back callouts as you can only have one Queueable Callout running at a time)

public class AsyncExecutionExample implements Queueable, Database.AllowsCallouts {
    public void execute(QueueableContext context) {
        //Do your 
        //SOQL to get sObject, 
        //Callout to create and get the ID from other system, 
        //Update sObject with ID
        //It can all happen in this one method.
    }
}

In your scheduled class, just instantiate the above Class and execute it!

public class ScheduledClass implements Schedulable {
    public void execute(SchedulableContext SC) {
        System.enqueueJob(new AsyncExecutionExample());
    }
}

I think that's all you have to do.