Scheduled Apex

 

Scheduled Apex:

Scheduled apex is all about to run a piece of apex code at some particular time within a period of time. Schedule apex in Salesforce is a class that runs at a regular interval of time. To schedule an apex class, we need to implement an interface Schedulable.

global class SampleSchedulerClass implements Schedulable {

global void execute(SchedulableContext SC) {

//Some code that would be called

  }

}

Apex Scheduler Limits

1. You can only have 100 scheduled Apex jobs at one time.

2. The maximum number of scheduled Apex executions per a 24-hour period is 250,000 or the number of user licenses in your organization multiplied by 200, whichever is greater.

3. Synchronous Web service callouts are not supported from Scheduled Apex.

What is an Apex Scheduler?

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.

What could be the use cases for Apex Scheduler?

1. Sending Periodic notifications to users.

2. Tasks related to real-time updates.

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

Ok. So, what are the prerequisites for the apex scheduler?

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

What is the parameter of the execute method ? - SchedulableContext 

What is SchedulableContext?

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.

And what would be the use of that Job ID?

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.

What happens after the class is scheduled?

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.

So, How can I schedule the apex class?

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

–> Go to Setup --->Apex Classes

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

The difference between the two ways is that in the system.schedule method we can also specify the minutes and seconds as well but using the UI we can just mention the hour of the day.

What are the arguments of the System.Schedule method?

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.

What is return type of system.schedule?

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

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

As you mentioned that the jobID can be used to query the progress, how can we track it?

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];

 

What is this CronJobDetailId?

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

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

1 2	CronTrigger job = [SELECT Id, CronJobDetail.Id, CronJobDetail.Name, CronJobDetail.JobType FROM CronTrigger where Id =: jobId];

OR

Can query on CronJobDetail with CronJobDetailId.

1 2	CronJobDetail ctd = [SELECT Id, Name, JobType  FROM CronJobDetail WHERE Id = :CronJobDetailId];

what is CRON_EXP?

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

Why is the purpose of special characters?

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

So let's say, I have scheduled an apex class to run at 7 pm today, and at 7 pm, some batches are already running. How will your apex class code run at 7 pm?

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.

Cool, let’s say, I have scheduled an apex class to run at 3 pm today, and at 3:15 pm, downtime occurred. What will happen now?

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.

What async processes, I 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)

Which of the above can cause an issue?

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.

Want to schedule batch job at one time only and not again. How to do it?

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.

How to get count of Apex Scheduled Job programmatically?

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, can you update the class or any classes referenced in Salesforce UI?

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

Maximum, How many jobs can be scheduled at any point in time?

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’

How to Call batch apex from schedulable class?

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.

How to get Job name and job type for Scheduled jobs?

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

Callout is not supported in Scheduled Apex so what is the alternative?

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.

How can you stop the execution of a job that has already been scheduled?

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

Can we write a Unit test case for a scheduled Apex?

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();     } }

Can you tell Best Practices to be followed while using Scheduled Apex?

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.

In a set list of emails are stored in execute method. In the finish method that set is not having any emails. What is the reason?

By default batch class is stateless. Emails which are added to set can be remembered only in execute method. If we try to access the set in finish method you won't see those emails. In finish method if you want to access those emails of that set we should inherit the interface called Database.Stateful.

How to schedule batch apex in minutes/hours?

To schedule the batch class in minutes/hours, in the finish method we should use System.schedule method which will take 3 parameters Job Name, Crone Expression and schedulable class instance name respectively.

SchedulableUsage su = new SchedulableUsage(); //Preparing chron_exp Datetime sysTime = System.now(); sysTime = sysTime.addminutes(6); String chron_exp = '' + sysTime.second() + ' ' + sysTime.minute() + ' ' + sysTime.hour() + ' ' + sysTime.day() + ' ' + sysTime.month() + ' ? ' + sysTime.year();           System.schedule('Dep Update'+sysTime.getTime(),chron_exp, su);