Parent to child creation using batch class

Question

I have written a batch class where when parent is created then child get created and relate to it. But when I manually create the parent record, child record get create in bulk.

I want when one parent is created then related to it one child should get created.

Below is the code:

Batch

global class ESRT_Batch_Tour_Email_Creation implements Database.Batchable <sObject> {
    List<Leasing_Tour_Email_Queue__c> Lea = new List<Leasing_Tour_Email_Queue__c>();
    
    global Database.QueryLocator start (Database.BatchableContext bc){
        String query = 'SELECT Id,Name,Tour_Date__c from Tour__c';
        return Database.getQueryLocator(query);
    }
    
    global void execute(Database.BatchableContext bc,List<Tour__c> batch) {
        for(Tour__c tou : batch){
            Leasing_Tour_Email_Queue__c t = new Leasing_Tour_Email_Queue__c();
            t.Tour__c = tou.Id;
            Lea.add(t);
        }

        insert lea;
    }

    global void finish(Database.BatchableContext bc) {
        //Do Nothing.
    }
}

Trigger

trigger LeasingTourBatc on Tour__c (after insert) {
    if (Trigger.isAfter && Trigger.isInsert){
       for(Tour__c To : Trigger.new){
           ESRT_Batch_Tour_Email_Creation b = new ESRT_Batch_Tour_Email_Creation();
           Database.executeBatch(b);
       }
    }
}

Answer 1

There are several problems with the code:

1. You are queueing one batch per record inserted which I don't think is what you want to achieve (also a bad practice). I assume that you want to enqueue a single batch that will process all the records that have been inserted
2. Your start() method of the Batch Class has no filtering. It is always querying for all the Tour__c records in the Database which is also incorrect

So, in order to fix this, you need to pass the records to the batch in some way and filter the query to only include the records that have been created. I've updated your code with these suggestions. I'm passing the records through the Constructor of the class.

Trigger

trigger LeasingTourBatc on Tour__c (after insert) {
    if (Trigger.isAfter && Trigger.isInsert){
           ESRT_Batch_Tour_Email_Creation b = new ESRT_Batch_Tour_Email_Creation(Trigger.new);
           Database.executeBatch(b);
       }
    }
}

Batch

global class ESRT_Batch_Tour_Email_Creation implements Database.Batchable <sObject> {

    List<Tour__c> createdTours;

    public ESRT_Batch_Tour_Email_Creation (List<Tour__c> createdTours) {
        this.createdTours = createdTours;
    }
    
    global Database.QueryLocator start (Database.BatchableContext bc){
        String query = 'SELECT Id,Name,Tour_Date__c from Tour__c where Id IN: createdTours';
        return Database.getQueryLocator(query);
    }
    
    global void execute(Database.BatchableContext bc,List<Tour__c> batch) {
        List<Leasing_Tour_Email_Queue__c> Lea = new List<Leasing_Tour_Email_Queue__c>();
        for(Tour__c tou : batch){
            Leasing_Tour_Email_Queue__c t = new Leasing_Tour_Email_Queue__c();
            t.Tour__c = tou.Id;
            Lea.add(t);
        }

        insert lea;
    }

    global void finish(Database.BatchableContext bc) {
        //Do Nothing.
    }
}

)

Answer 2

First of all, if it's a minor 1:1 creation, you probably don't need Batchable. That's for mass updates. Secondly, you've written your query without a filter, so naturally, it will create one child record for every parent in the database each time you create one parent. Further, you're creating one batch per record in the trigger context, so you could end up running a hundred batches in a single trigger. If you really need the extra CPU time, use Queueable for a task of this size. Also, do not use global unless this is for a managed package, and you need subscribers to call it directly. public is the recommended access level for this code.

public class ESRT_Batch_Tour_Email_Creation implements Queueable {
    Tour__c[] tours;
    public ESRT_Batch_Tour_Email_Creation(Tour__c[] records) {
        tours = records;
    }
    public void execute(QueueableContext context) {
        Leasing_Tour_Email_Queue__c[] lea = new Leasing_Tour_Email_Queue__c[0];
        for(Tour__c tou : tours){
            Leasing_Tour_Email_Queue__c t = new Leasing_Tour_Email_Queue__c();
            t.Tour__c = tou.Id;
            Lea.add(t);
        }
        insert lea;
    }    
}

Which would make your trigger:

trigger LeasingTourBatc on Tour__c (after insert) {
    ESRT_Batch_Tour_Email_Creation b = new ESRT_Batch_Tour_Email_Creation(Trigger.new);
    System.enqueueJob(b);
}