Batch Apex and Schedular

About Batch Apex

Implementing the Database.Batchable Interface

The Database.Batchable interface contains three methods that must be implemented:

• start method

global (Database.QueryLocator | Iterable<sObject>) start(Database.BatchableContext bc)

{}

The start method is called at the beginning of a batch Apex job. Use the start method to collect the records or objectsto be passed to the interface method execute.This method returns either a Database.QueryLocator  object or an iterable that contains the records or objects being passed into the job.

Custom Cloud Batch ApexUse the Database.QueryLocator object when you are using a simple query (SELECT) to generate the scope of objects used in the batch job. If you use a QueryLocator object, the governor limit for the total number of records retrieved by SOQL queries is bypassed. For example, a batch Apex job for the Account object can return a QueryLocator for all account records (up to 50 million records) in an organization. Another example is a sharing recalculation for the Contact object that returns

a QueryLocator for all contact records in an organization. Use the iterable when you need to create a complex scope for the batch job. You can also use the iterable to create your own custom process for iterating through the list. Important: If you use an iterable, the governor limit for the total number of records retrieved by SOQL queries is still enforced.

• execute method:

global void execute(Database.BatchableContext BC, list<P>){}

The execute method is called for each batch of records passed to the method. Use this method to do all required processing

for each chunk of data.

This method takes the following:

- A reference to the Database.BatchableContext object.

- A list of sObjects, such as List<sObject>, or a list of parameterized types. If you are using a Database.QueryLocator, the returned list should be used.

• finish method

global void finish(Database.BatchableContext BC){}

The finish method is called after all batches are processed. Use this method to send confirmation emails or execute post-processing operations.

Each execution of a batch Apex job is considered a discrete transaction. For example, a batch Apex job that contains 1,000

records and is executed without the optional scope parameter from Database.executeBatch is considered five transactions

of 200 records each.The Apex governor limits are reset for each transaction. If the first transaction succeeds but the second

fails, the database updates made in the first transaction are not rolled back.

Apex Scheduler—Limited Release

You asked for it! This enhancement is an idea from the IdeaExchange.

Available in: Unlimited, Developer, and Enterprise Editions

You can schedule Apex classes to run at specific times. First implement the Schedulable interface for the class, then specify

the schedule using either the Schedule Apex page in the Salesforce.com user interface, or the System.schedule method.

In addition, you can use the new method System.abortJob to stop a job after it has been scheduled.

Note: The Apex scheduler is currently available through a limited release program. Contact salesforce.com to verify

if your organization can participate in the limited release program.

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Custom Cloud Apex Scheduler—Limited ReleaseImplementation Tips

• You must implement the Schedulable interface for the class first before you can schedule the class.

• Use either the System.schedule method or the Schedule Apex page in the Salesforce.com user interface to schedule

the class.

• After you schedule a job, you can monitor the progress of the job on the All Scheduled Jobs page.

• Salesforce.com only adds the process to the queue at the scheduled time. Actual execution may be delayed based on service

availability.

• Once the job has completed, you can see specifics about the job (such as whether it passed or failed, how long it took to

process, the number of records process, and so on) on the Apex Jobs page.

• The System.schedule method uses the user's timezone for the basis of all schedules.

• Use the System.abortJob to stop jobs that were scheduled using System.schedule.

Best Practices

• Use extreme care if you are planning to schedule a class from a trigger. You must be able to guarantee that the trigger will

not add more scheduled classes than the ten that are allowed. In particular, consider API bulk updates, import wizards,

mass record changes through the user interface, and all cases where more than one record can be updated at a time.

• Though it's possible to do additional processing in the execute method,Salesforce.com recommends that all processing

take place in a separate class.

About Apex Scheduler

Implementing the Schedulable Interface

To schedule an Apex class to run at regular intervals, first write an Apex class that implements the Salesforce.com-provided

interface Schedulable.

To monitor or stop the execution of a scheduled Apex job using the Salesforce.com user interface, click Setup➤ Monitoring

➤ Scheduled Jobs. For more information, see “Monitoring Scheduled Jobs” in the Salesforce.com online help.

To stop execution of a job that was scheduled using the System.schedule method, use the System.abortJob method.

The Schedulable interface contains one method that must be implemented, execute.

global void execute(SchedulableContext sc){}

Use the SchedulableContext object to keep track of the scheduled job once it's scheduled.The SchedulableContext method

getTriggerId returns the Id of the CronTrigger object associated with this scheduled job as a string. Use this method to

track the progress of the scheduled job.

Use this method to instantiate the class you want to schedule.

Tip: Though it's possible to do additional processing in the execute method, Salesforce.com recommends that all

processing take place in a separate class.

The following example implements the Schedulable interface for a class called mergeNumbers:

global class scheduledMerge implements Schedulable{

global void execute(SchedulableContext SC) {

mergeNumbers M = new mergeNumbers();

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Custom Cloud Apex Scheduler—Limited Release}

}

The following example uses the System.Schedule method to implement the above class.

scheduledMerge m = new scheduledMerge();

String sch = '20 30 8 10 2 ?';

system.schedule('Merge Job', sch, m);

You can also use the Schedulable interface with batch Apex classes.The following example implements the Schedulable

interface for a batch Apex class called batchable:

global class scheduledBatchable implements Schedulable{

global void execute(SchedulableContext sc) {

batchable b = new batchable();

database.executebatch(b);

}

}

Using the System.Schedule Method

Note: The Apex scheduler is currently available through a limited release program. Contact salesforce.com to verify

if your organization can participate in the limited release program.

After you implement a class with the Schedulable interface, use the System.Schedule method to execute it.

Note: Use extreme care if you are planning to schedule a class from a trigger. You must be able to guarantee that the

trigger will not add more scheduled classes than the ten that are allowed. In particular, consider API bulk updates,

import wizards, mass record changes through the user interface, and all cases where more than one record can be

updated at a time.

The System.Schedule method takes three arguments: a name for the job, an expression used to represent the time and

date the job is scheduled to run, and the name of the class.This expression has the following syntax:

Seconds Minutes Hours Day_of_month Month Day_of_week optional_year

Note: Salesforce.com only adds the process to the queue at the scheduled time. Actual execution may be delayed based

on service availability.

The System.Schedule method uses the user's timezone for the basis of all schedules.

The following are the values for the expression:

Name Values Special Characters

Seconds 0–59 None

Minutes 0–59 None

Hours 0–23 , - * /

Day_of_month 1–31 , - * ? / L W

Month 1–12 or the following: , - * /

• JAN

• FEB

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Custom Cloud Apex Scheduler—Limited ReleaseName Values Special Characters

• MAR

• APR

• MAY

• JUN

• JUL

• AUG

• SEP

• OCT

• NOV

• DEC

Day_of_week 1–7 or the following: , - * ? / L #

• SUN

• MON

• TUE

• WED

• THU

• FRI

• SAT

optional_year null or 1970–2099 , - * /

The special characters are defined as follows:

• , —Delimits values. For example, use JAN, MAR, APR to specify more than one month.

• - —Specifies a range. For example, use JAN-MAR to specify more than one month.

• * —Specifies all values. For example, if Month is specified as *, the job is scheduled for every month.

• ? —Specifies no specific value.This is only available for Day_of_month and Day_of_week, and is generally used when

specifying a value for one and not the other.

• / —Specifies increments.The number before the slash specifies when the intervals should begin, and the number after

the slash is the interval amount. For example, if you specify 1/5 for Day_of_month, the Apex class runs every fifth day

of the month, starting on the first of the month.

• L —Specifies the end of a range (last).This is only available for Day_of_month and Day_of_week. When used with

Day of month, L always means the last day of the month, such as January 31, February 28 for leap years, and so on.

When used with Day_of_week by itself, it always means 7 or SAT. When used with a Day_of_week value, it means the

last of that type of day in the month. For example, if you specify 2L, you are specifying the last Monday of the month. Do

not use a range of values with L as the results may be unexpected.

• W —Specifies the nearest weekday (Monday-Friday) of the given day.This is only available for Day_of_month. For

example, if you specify 20W, and the 20th is a Saturday, the class runs on the 19th. If you specify 1W, and the first is a

Saturday, the class does not run in the previous month, but on the third, which is the following Monday.

Tip: Use the L and W together to specify the last weekday of the month.

• # —Specifies the nth day of the month, in the format weekday#day_of_month.This is only available for Day_of_week.

The number before the # specifies weekday (SUN-SAT).The number after the # specifies the day of the month. For

example, specifying 2#2 means the class runs on the second Monday of every month.

146

Custom Cloud Apex Scheduler—Limited ReleaseThe following are some examples of how to use the expression.

Expression Description

0 0 13 * * ? Class runs every day at 1 P.M.

0 0 22 ? * 6L Class runs the last Friday of every month at 10 P.M.

0 0 10 ? * MON-FRI Class runs Monday through Friday at 10 A.M.

0 0 20 * * ? 2010 Class runs every day at 8 P.M. during the year 2010.

In the following example, the class proschedule implements the Schedulable interface.The class is scheduled to run at

8 A.M., on the 13th of February.

proschedule p = new proschedule();

String sch = '0 0 8 13 2 ?';

system.schedule('One Time Pro', sch, p);

Scheduling Apex

Available in: Unlimited, Developer, and Enterprise Editions

Note: The Apex scheduler is currently available through a limited release program. Contact salesforce.com to verify

if your organization can participate in the limited release program.

Use the Apex scheduler if you have specific Apex classes that you want to run on a regular basis, or to run a batch Apex job

using the Salesforce.com user interface.

Important: Salesforce.com only adds the process to the queue at the scheduled time. Actual execution may be delayed

based on service availability.

To schedule jobs using the Apex scheduler:

1. Implement the Schedulable interface in an Apex class that instantiates the class you want to run.

2. Click Setup ➤ Develop ➤ Apex Classes and click Schedule Apex.

3. Specify the name of a class that you want to schedule.

4. Specify how often the Apex class is to run.

• For Weekly—specify one or more days of the week the job is to run (such as Monday and Wednesday).

• For Monthly—specify either the date the job is to run or the day (such as the second Saturday of every month.)

5. Specify the start and end dates for the Apex scheduled class. If you specify a single day, the job only runs once.

6. Specify a preferred start time.The exact time the job starts depends on what other jobs are in the queue at that time.

7. Click Save.

Note: You can only have ten active or scheduled jobs concurrently.

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Custom Cloud Apex Scheduler—Limited ReleaseAfter you schedule an Apex job, you can monitor the progress of the job on the All Scheduled Jobs page.

Once the job has completed, you can see specifics about the job (such as whether it passed or failed, how long it took to process,

the number of records process, and so on) on the Apex Jobs page.