Explain chaining of Batch Jobs in Salesforce?

Before API version 26.0 it was not possible to start another batch job from an existing batch job. Starting with API version 26.0, you can start another batch job from an existing batch job to chain jobs together.

Chain a batch job is useful when you want to start a job after another one finishes and when your job requires batch processing, such as when processing large data volumes. Otherwise, if batch processing isn’t needed, consider using Queueable Apex.

Let’s us understand with a real time example of how to invoke a batch apex from another batch apex.  

The provided code defines two Salesforce Apex batch classes, BatchClassToUpdateAccountIndustry and BatchClassToUpdateContactIndustry, demonstrating a sequence of data processing tasks.

The provided code represents two Salesforce Apex batch classes designed to update the Industry field on Account and Contact records. Here's a short description of the code:

These batch classes work together to update the Industry field on Account where Type is Technology Partner and all contacts where Account Industry is Communications, ensuring that all Contacts have Industry as Communications where Account Industry is Communications. The second batch class is invoked from the finish method of the first batch class to maintain the sequence of updates.

global class BatchClassToUpdateAccountIndustry implements Database.Batchable<sObject> {

 String query = 'Select Id,Name,Rating, Industry,Type from Account WHERE (Type = \'Technology Partner\') ';

 String accIndustry='Communications';

 List<Account> upddateAccount= new List<Account>();

 global Database.QueryLocator start(Database.BatchableContext bc) {

 

 return Database.getQueryLocator(query);

 }

 

 global void execute(Database.BatchableContext bc, List<Account> records){

 

    System.debug('records'+records.size());

    for (Account accountobj : records) {

          accountobj.Industry = accIndustry;

          upddateAccount.add(accountobj);

        }

        try{

        update upddateAccount;

        }

        catch(Exception e){

        System.debug('Error is '+e.getMessage());

        }

 }

 

 global void finish(Database.BatchableContext bc){

 //Note: We are calling second batch class i.e BatchClassToUpdateContactRating from Finish Method of this batch.

 BatchClassToUpdateContactIndustry b = new BatchClassToUpdateContactIndustry ();

 Database.executeBatch(b, 200);

 }

 }

 

global class BatchClassToUpdateContactIndustry implements Database.Batchable<sObject> {

List<Contact> updatedContacts= new List<Contact>();

 String query = 'Select FirstName, LastName,Account.Rating from Contact WHERE (Account.Industry = \'Communications\') ';

 global Database.QueryLocator start(Database.BatchableContext bc) {

 return Database.getQueryLocator(query);

 }

 global void execute(Database.BatchableContext bc, List<Contact> records){

 for(Contact con : records){

 con.Industry__c ='Communications';

 updatedContacts.add(con);

 }

 update updatedContacts;

 }

 global void finish(Database.BatchableContext bc){

 

 }

 }

Now, let’s test the working of the above batch classes.

Open execute anonymous window and paste the below code and click execute.

BatchClassToUpdateAccountIndustry batchObj= new BatchClassToUpdateAccountIndustry();

Database.executebatch(batchObj,200);

Now, we can verify one of the account where the type is technology partner to check if account industry and contact industry is updated or not as shown below.