Batch apex with no query in start method?

Question

I have a method in an Apex class which is used in a visualforce page. I have been asked to move part of the method's code in a batch, since it seems that it is exceeding limits and causing errors.

Here is the code:

@RemoteAction
public static Map<String, String> create(List <Map<String, String>> contactRecords, String campaignId, String caseType, String caseSubType) {
    Map<String, String> result = new Map<String, String>();   
    List<Case> cases = new List<Case>();
    List<CampaignMember> cmList = new List<CampaignMember>();
    
    for (Map<String, String> contactRecord : contactRecords) {
        String contactId = contactRecord.get('Id ');
        if(campaignId != null && contactId != null){
            CampaignMember currentCamp = new CampaignMember(ContactId=Id.valueOf(contactId), CampaignId=campaignId);
            Case currentCase = new Case(Status='In Progress', unig__Channel__c='TELEMARKETING', Origin='Web',unig__Campaign__c=campaignId, ContactId=Id.valueOf(contactId), UNITA_Case_Type__c =caseType, UNITA_Case_Subtype__c = caseSubType, UNITA_From_Einstein__c=true);
            cases.add(currentCase);
            cmList.add(currentCamp);
            //System.debug('### currentCamp ' + currentCamp);
        }
    }
    try{
        //System.debug('### CAMPAING MEMBER LIST ' + cmList.size());
        //System.debug('### CASES LIST ' + cases.size());
        insert cmList;
        insert cases;
    }catch(Exception e){
        System.debug('### ERROR ' + e);
    }        
    
    for (Case currentCase2 : cases) {
        String currentCaseContactId = currentCase2.contactId;
        String currentCaseId = currentCase2.Id;
        result.put(currentCaseContactId, currentCaseId);
    }
    return result;
}

My question is: how do I implement the start method in the batch? I don't need a query, since the contacts are passed to the function as a parameter? How can the batch work with no query in the start method.

I have no experience at all with batches, so I might be missing something. Any help is much appreciated!

Answer 1

If you want to batch over a specific set of records, you still need a query. But you can pass in the Id values to a constructor or similar and store them in memory for later use in a query filter.

public class MyBatch implements Database.Batchable<SObject>
{
    final Set<Id> recordIds;
    public MyBatch(Set<Id> recordIds)
    {
        this.recordIds = recordIds;
    }
    
    public Database.QueryLocator start(Database.BatchableContext context)
    {
        return [SELECT ... FROM Contact WHERE Id IN :recordIds];
    }
    // other batch methods
}

Answer 2

Don't use Batchable if you just need more CPU time. Instead, use Queueable. The translation is pretty straight-forward:

public class AsyncProcessor implements Queueable {
    List <Map<String, String>> contactRecords;
    String campaignId;
    String caseType;
    String caseSubType;
    public AsyncProcessor(List <Map<String, String>> contactRecords, String campaignId, String caseType, String caseSubType) {
        this.contactRecords = contactRecords;
        this.campaignId = campaignId;
        this.contactRecords = contactRecords;
        this.caseType = caseType;
    }
    public void execute(QueueableContext context) {
        Map<String, String> result = new Map<String, String>();   
        List<Case> cases = new List<Case>();
        List<CampaignMember> cmList = new List<CampaignMember>();
        
        for (Map<String, String> contactRecord : contactRecords) {
            String contactId = contactRecord.get('Id ');
            if(campaignId != null && contactId != null){
                CampaignMember currentCamp = new CampaignMember(ContactId=Id.valueOf(contactId), CampaignId=campaignId);
                Case currentCase = new Case(Status='In Progress', unig__Channel__c='TELEMARKETING', Origin='Web',unig__Campaign__c=campaignId, ContactId=Id.valueOf(contactId), UNITA_Case_Type__c =caseType, UNITA_Case_Subtype__c = caseSubType, UNITA_From_Einstein__c=true);
                cases.add(currentCase);
                cmList.add(currentCamp);
                //System.debug('### currentCamp ' + currentCamp);
            }
        }
        try{
            //System.debug('### CAMPAING MEMBER LIST ' + cmList.size());
            //System.debug('### CASES LIST ' + cases.size());
            insert cmList;
            insert cases;
        }catch(Exception e){
            System.debug('### ERROR ' + e);
        }        
        // Can't return the values from this context, though...
        for (Case currentCase2 : cases) {
            String currentCaseContactId = currentCase2.contactId;
            String currentCaseId = currentCase2.Id;
            result.put(currentCaseContactId, currentCaseId);
        }    
    }
}

@RemoteAction
public static void create(List <Map<String, String>> contactRecords, String campaignId, String caseType, String caseSubType) {
    System.enqueueJob(new AsyncProcessor(contactRecords, campaignId, caseType, caseSubType));
}

However, the problem with this is that you won't be able to get the results back. You'll have to deliver them via a separate mechanism, as Queueable/Batchable/Schedulable/future methods all run asynchronously. They won't help you solve your current situation, I think.

You may need to refactor your code to work as you'd like and get a response back. Perhaps consider writing your code to upload batches from the client side. I once wrote some code like this (I don't have it, so I can't share, unfortunately) where the client would adjust the batch size dynamically.