Solution on Calling queueable from Batch causing exception of "System.LimitException: Too many queueable jobs added to the queue: 2"

Question

Have any one of you come across a situation, where I need to call queueable class from batch. To give you more details, let us a scenario - I have a scheduler, which will run after particular time of interval; which will call a batch method withing its execute method. Lets say batch of Cases which needs to processed.

In batch for each entry, we need to have 1 callout + process data 1 callout + DML in sync.

We tried following thing:

Batch class:

lObject = List of object(which needs to be processed)

    for(Object o: lObject)
    {
        if( Limits.getQueueableJobs() <= 25) 
        {
            System.debug('in batch class  limits : ' + Limits.getQueueableJobs() );
            System.enqueueJob(new queueableClass(o));    
        }
        else break;
    }

Queueable Class:

1. callout1
2. processData
3. Again enqueue- newEnqueueClass
4. newEnqueueClass : Insert data
5. future callout [since we cannot have callout after DML].

PS:For some reason, we cannot bulkify callout(due to 3rd party system limitation).

What should be ideal solution to this problem?

Answer 1

Assuming you can't refactor to allow things to happen for you, how about using this pattern:

public interface Action
{
    void execute();
}

public class CalloutPlusDMLAction implements Action
{
    private Id recordId;
    public CalloutPlusDMLAction(Id recordId)
    {
        this.recordId = recordId;
    }
    public void execute()
    {
        // make callout to 3rd party system
        // do your dml
    }
}

public class QueueableAction implements Action
{
    private Id recordId;
    public QueueableAction(Id recordId)
    {
        this.recordId = recordId;
    }
    public void execute()
    {
         System.enqueueJob(new YourQueueable(recordId));
    }
}

public class ActionBatch implements Database.Batchable<Object>, Database.AllowsCallouts
{
    public Iterable<Object> start( Database.BatchableContext bc )
    {
        List<Action> actions = new List<Action>();
        for(Case ocase : [SELECT Id FROM Case])
        {
            actions.add(new CalloutPlusDMLAction(oCase.Id));
            actions.add(new QueueableAction(oCase.Id));
        }
        return (Iterable<Object>)actions;
    }
    public void execute(Database.BatchableContext BC, List<Object> scope) 
    {
        for(Action action : (List<Action>)scope)
        {
            action.execute();
        }
    }
    public void finish(Database.BatchableContext bc){}
}

Then, set your batch size to 1 and call as follows:

Database.executeBatch( new ActionBatch(), 1 );

For each iteration of execute() you'll get the web service callout and DML happening first, followed by the queueable in the next iteration. Or perhaps you won't even need your queueable by separating each execution context using batch size of 1.