Interview Questions on Scheduled Apex in Salesforce

 Apex Scheduler is an ability to invoke an Apex class to run at specific times.
To schedule an apex class, we need to implement an interface Schedulable.

1. Sending Periodic notifications to users.

2. Tasks related to real-time updates.

3. Newsletter's on the 15th of every month.

 The apex class needs to implement the Salesforce-provided interface Schedulable and override it’s execute() method.

 The parameter of this method is a SchedulableContext object.

global class SampleSchedulerClass implements Schedulable {
 global void execute(SchedulableContext SC)
  {
    /* Logic goes here */
  }
}

  Represents the parameter type of a method in a class that implements the Schedulable interface and contains the scheduled job ID using the getTriggerID() method. This interface is implemented internally by Apex.

 With that ID, we can track the Progress of a Scheduled Job through a query on CronTrigger. The ID is of type CronTrigger.

Moreover, we can go to Setup ---> Scheduled Jobs too, for monitoring.

 After a class has been scheduled, a CronTrigger object is created that represents the scheduled job. It provides a getTriggerId method that returns the ID of a CronTrigger API object.

 Once you are done with the implementation. You can schedule it either through the
Developer console using system.schedule method.

SampleSchedulerClass obj = new SampleSchedulerClass();
String CRON_EXP = '20 30 8 10 2 ?';
String jobID = system.schedule(‘Sample Scheduler Job’, CRON_EXP, obj);

Here:
20 represents seconds
30 represents minutes
8 represents hour of the day
10 represents 10th day of month
2 represents month of the year
? represents day of the month

OR

From system UI
 1. From Setup, enter Apex in Quick Find box
 2. Select Apex Classes

–> Go to Setup --->Apex Classes page

You will see a “Schedule Apex” button. You can set up the timing from there.

 Once you are implemented schedulable interface use system.schedulable method to execute the class.

system.schedule() method takes 3 parameters :

1. Name of the job.
2. An expression that is used to represent the time and date of the operation.
3. The object of the class which you want to execute.

 System.schedule method returns the job ID in string format.

String jobID = system.schedule(‘Sample Scheduler Job’, CRON_EXP, obj);

 We can simply fire a query to get information about current job.

CronTrigger ct = [SELECT CronExpression, CronJobDetailId, PreviousFireTime, 
TimesTriggered, NextFireTime, State, StartTime, EndTime 
FROM CronTrigger WHERE Id =: jobID];

 CronJobDetail is the parent CronTrigger that saves a job’s information like Name, JobType, etc.

JobType value is always 7 for Scheduled Apex.

we can get these details too using the same CronTrigger query.

CronTrigger job = [SELECT Id, CronJobDetail.Id, CronJobDetail.Name, CronJobDetail.JobType 
FROM CronTrigger where Id =: jobId];

OR

Can query on CronJobDetail with CronJobDetailId.

CronJobDetail ctd = [SELECT Id, Name, JobType 
 FROM CronJobDetail WHERE Id = :CronJobDetailId];

 It is called CRON EXPRESSION which is used to define the scheduling time. it has 6 to 7 inputs.

An expression is written in the form of 'Seconds, Minutes, Hours, Day_of_month, Month, Day_of_week, optional_year'.

it uses some special characters too

? — No Value
* — All Values
? — Specifies no specific value
/-Specifies increments. The number before the slash specifies when the intervals will begin, and the number after the slash is the interval amount.
#-Specifies the nth day of the month, in the format weekday#day_of_month
L-Specifies the end of a range (last)
W-Specifies the nearest weekday(Monday-Friday) of the given day

Values of Expressions in Salesforce Apex

 The purpose of special characters is to define a range or interval. They are like wildcard characters in database queries.

For example, If I want to run a job at 12 midnight on the 1st of every month in 2022.
My CRON_EXP would be : “0 0 0 1 * 2022”

Where * = all values possible for a month i.e. 1–12

 It will get scheduled on time because Salesforce schedules the class for execution at the specified time, But the Actual execution may be delayed based on service availability. So, it will run once everything is done.

 There could be 2 cases:

1. Before starting the job, downtime occurred, in this case, Apex jobs will be scheduled to run after the service comes back up, when system resources become available.

2. If a scheduled Apex job was running when downtime occurred, the job is rolled back and scheduled again after the service comes back up.

 We can schedule:

1. Batch Apex (can call a batch from Scheduled Apex)
2. Future Method (can call future from Scheduled Apex)
3. Queueable Apex (can call queueable form Scheduled Apex)

 Calling the Future methods from scheduled apex can cause some issue:

1. The future won’t guarantee it’s execution on time, so tracking is not possible. Also, we lose transaction control because the scheduled apex gets over as soon as it fires the future method call.

2. There is a limit to the number of future calls based on your number of licenses.

 System.scheduleBatch() is used to run a schedule a batch job only once for a future time. This method has got 3 parameters.

param 1 : Instance of a class that implements Database.Batchable interface.
param 2 : Job name.
param 3 : Time interval after which the job should start executing.
param 4 : It’s an optional parameter which will define the no. of that processed at a time.

The system.scheduleBatch() returns the scheduled job Id.

We can use the job Id to abort the job.

This method returns the scheduled job ID also called CronTrigger ID.

String cronID = System.scheduleBatch(reassign, 'job example', 1);

CronTrigger ct = [SELECT Id, TimesTriggered, NextFireTime 
                   FROM CronTrigger WHERE Id = :cronID];

This method is available only for batch classes and doesn’t require the implementation of the Schedulable interface. This makes it easy to schedule a batch job for one execution.

 You can programmatically query the CronTrigger and CronJobDetail objects to get the count of Apex scheduled jobs.

 If there are one or more active scheduled jobs for an Apex class, you cannot update the class or any classes referenced by this class through the Salesforce user interface. However, you can enable deployments to update the class with active scheduled jobs by using the Metadata API

 You can only have 100 scheduled Apex jobs at one time. Either we can verify the count by viewing the Scheduled Jobs page.

OR

we can simply query with CronJobDetail.JobType as 7 (scheduled Apex) on CronTrigger>

SELECT COUNT() FROM CronTrigger WHERE CronJobDetail.JobType = ‘7’

 Create instance of batchClass and then pass the instance in database.executebatch.

batchable b = new batchable();
 database.executebatch(b);

An easier way to schedule a batch job is to call the System.scheduleBatch method without having to implement the Schedulable interface.

 You can get job’s name and the job’s type from the CronJobDetail record associated with the CronTrigger record.

 Synchronous Web service callouts are not supported from scheduled Apex. To be able to make callouts, make an asynchronous callout by placing the callout in a method annotated with @future(callout=true) and call this method from scheduled Apex. However, if your scheduled Apex executes a batch job, callouts are supported from the batch class.

 To stop the execution of a job that has been scheduled, use the System.abortJob method with the ID returned by the getTriggerID method.

 Yes we can.

Use the Test methods startTest and stopTest around the System.schedule method to ensure it finishes before continuing your test.

All asynchronous calls made after the startTest method are collected by the system.

When stopTest is executed, all asynchronous processes are run synchronously.

If you don’t include the System.schedule method within the startTest and stopTest methods, the scheduled job executes at the end of your test method

Apex Class

global class ScheduledApexTestExample implements Schedulable {
    // This test runs a scheduled job at midnight Sept. 19th. 2022
    public static String CRON_EXP = '0 0 0 19 9 ? 2022';
    global void execute(SchedulableContext ctx) {
    }   
}

Test Class

@istest
class TestClass {
    static testmethod void test() {
        Test.startTest();
        String jobId = System.schedule('testBasicScheduledApex',
                                       ScheduledApexTestExample.CRON_EXP, 
                                       new ScheduledApexTestExample());
        // Get the information from the CronTrigger API object
        CronTrigger ct = [SELECT Id, CronExpression, TimesTriggered, 
                          NextFireTime FROM CronTrigger WHERE id = :jobId];
        // Verify the expressions are the same
        System.assertEquals(ScheduledApexTestExample.CRON_EXP, ct.CronExpression);
        Test.stopTest();
    }
}

1. Synchronous Web service callouts are not supported from scheduled Apex. To be able to make callouts, make an asynchronous callout.

2. While scheduling a job from the trigger, we must be able to guarantee that the trigger won’t add more scheduled classes than the limit.