Introduction

Scheduling is used to execute the Apex code in the background at specific times

Steps To Create A Schedulable Batch Apex Class

We have three steps to create a Schedulable Batch Apex Class.

1. First, we need to write a Batch Class that we want to schedule
2. After this, write a schedulable batch apex class that contains the code to execute the Batch Class
3. In the end, we need to schedule the scheduled apex class either from the Developer Console or from the Apex Scheduler User Interface (UI)

Write A Batch Class

A class that implements Database.Batchable interface is a Batch Class. This Interface includes 3 methods to which the implementing class needs to give a body. The first is the start method which collects the records on which processing needs to be done by Batch Apex and returns a Database.QueryLocator. Then, we have execute method, which does processing on records and returns void. The last method is finish which also returns void and is called post-batch processing

Example:

Write a Batch Class to Update the Status of the Campaign to Completed if it is not Completed.

public class BatchClassCampComplStatus implements Database.batchable {
//collects the record using the query
public Database.QueryLocator start(Database.BatchableContext bc){
String query = 'SELECT Id, Name, Status, EndDate FROM Campaign WHERE Status != \'Completed\'';
return Database.getQueryLocator(query);
}
//processing of records takes place in execute method
public void execute(Database.BatchableContext bc, List camp){
List campList = new List();
for(Campaign cc : camp){
if(cc.Status != 'Completed'){
cc.Status = 'Completed';
campList.add(cc);
}
}
update campList;
}
//post batch processing code
// called at the end
public void finish(Database.BatchableContext bc){
System.debug('Batch Job Completed Successfully.');


}
}

Write A Schedulable Batch Apex Class

Scheduling is mainly done for data clean-up or weekly maintenance tasks.

A class needs to implement a Schedulable interface and give the body to execute a method that returns void.

Example:

public class SchedulableClass implements Schedulable {
public void execute(SchedulableContext ctx){
BatchClassCampComplStatus bccs = new BatchClassCampComplStatus();
Id batchId = Database.executeBatch(bccs, 200);
}
}

Scheduling the Schedulable Batch Apex Class

There are two ways in which classes can be scheduled. One way is Apex Scheduler UI.

Path: Setup -> Apex Classes -> Click Schedule Apex Button

Another way is using cron expression in the developer console

CRON Expression

SchedulableClass sc = new SchedulableClass();

String cronExp = ‘0 0 8 * * ?’;

System.schedule(‘ScheduleBatchDemo’, cronExp, sc);