Friday, June 10, 2016

Batch Apex using Querylocator and iterable

Batch Apex using Querylocator and iterable

How to write Batch Class in Salesforce.com Apex

In order for us to write batch classes in apex, let us 1st understand what is batch class , when and where it should be used? This is an extensive blog going into details.

Main sections of this post are
1.                   What is batch Apex
2.                   When to use batch apex
3.                   Advantages of using batch apex
4.                   Batch Apex Governor limits
5.                   Sample Code

What is Batch Apex ?
Batch as the name suggests, is used when a large data (bulk) volume is involved and it has to be redundantly processed using a particular logic.
The Batch apex, can be used to conveniently perform time to time task and some real complex job ranging from data cleansing, archiving the data to the other quality improvements.  
When to use Batch Apex?
The typical use of batch apex is when you want to do a bulk job, but if you do it in a regular apex you’re bound to hit the governor limits. Batch Classes process the set of records you pass to it in batches of maximum 200 per batch. 
Advantages of using Batch Apex?
  Higher Governor Limits
  Can be used to process in batches
  Can be scheduled to run at different time. (read more)
  Work around to other governor limits e.g. Send More than 10 E-mails blog by Ankit Arora
here is the governor limit difference in using batch

Area
Normal Context
Batch Context
SOQL queries
100 SOQL per cycle
200 SOQL per cycle
records retrieved by SOQL queries
50,000
50,000,000 (getQueryLocator)
executed code statements
200,000
1,000,000
Heap size
6 MB
12 MB

Batch Apex Governor Limits

These are the governor Limits you need to keep in mind when dealing with Batch Apex
·                     Up to five queued or active batch jobs are allowed for Apex.
·                     A user can have up to 50 query cursors open at a time. For example, if 50 cursors are open and a client application still logged in as the same user attempts to open a new one, the oldest of the 50 cursors is released. Note that this limit is different for the batch Apex start method, which can have up to five query cursors open at a time per user. The other batch Apex methods have the higher limit of 50 cursors. Cursor limits for different Force.com features are tracked separately. For example, you can have 50 Apex query cursors, 50 batch cursors, and 50 Visual force cursors open at the same time.
·                     A maximum of 50 million records can be returned in the Database.QueryLocator object. If more than 50 million records are returned, the batch job is immediately terminated and marked as Failed.
·                     If the start method returns a QueryLocator, the optional scope parameter ofDatabase.executeBatch can have a maximum value of 2,000. If set to a higher value, Salesforce chunks the records returned by the QueryLocator into smaller batches of up to 2,000 records. If the start method returns an iterable, the scope parameter value has no upper limit; however, if you use a very high number, you may run into other limits.
·                     If no size is specified with the optional scope parameter of Database.executeBatch, Salesforce chunks the records returned by the start method into batches of 200, and then passes each batch to the execute method. Apex governor limits are reset for each execution of execute.
·                     The start, execute, and finish methods can implement up to 10 callouts each.
·                     Batch executions are limited to 10 callouts per method execution.
·                     The maximum number of batch executions is 250,000 per 24 hours.
·                     Only one batch Apex job's start method can run at a time in an organization. Batch jobs that haven’t started yet remain in the queue until they're started. Note that this limit doesn't cause any batch job to fail and execute methods of batch Apex jobs still run in parallel if more than one job is running.

Sample Code
Batch Class :
   1:  global class ExampleBatchClass implements Database.Batchable<sObject>{
   2:    
   3:        global ExampleBatchClass(){
   4:                   // Batch Constructor
   5:        }
   6:       
   7:        // Start Method
   8:        global Database.QueryLocator start(Database.BatchableContext BC){
   9:         return Database.getQueryLocator(query);
  10:        }
  11:      
  12:      // Execute Logic
  13:       global void execute(Database.BatchableContext BC, List<sObject> scope){
  14:              // Logic to be Executed batch wise      
  15:     
  16:       }
  17:     
  18:       global void finish(Database.BatchableContext BC){
  19:            // Logic to be Executed at finish
  20:       }
  21:    }

Call the Batch Class : 
   1:   ExampleBatchClass b = new ExampleBatchClass(); 
   2:         //Parameters of ExecuteBatch(context,BatchSize)
   3:          database.executebatch(b,10);



Note : if batch size is not mentioned it is 200 by default.

That’s about it for this post, if you still want a deep dive into Batch Classes I suggest you read this

Do let me know your thoughts Happy Coding !

How to use Batch Apex in Salesforce


Batch Apex in Salesforce 
As you all might know about the Salesforce governer limits on its data. When you want to fetch thousands of records or fire DML on thousands of rows on objects it is very complex in salesforce  and it does not allow you to operate on more than certain number of records which satisfies the Governer limits.
But for medium to large enterprises, it is essential to manage thousands of records every day. Adding/editing/deleting them when needed.
Salesforce has come up with a powerful concept called Batch Apex. Batch Apex allows you to handle more number of records and manipulate them by using a specific syntax.
We have to create an global apex class which extendsDatabase.Batchable Interface because of which the salesforce compiler will know, this class incorporates batch jobs. Below is a sample class which is designed to delete all the records of Account object (Lets say your organization contains more than 50 thousand records and you want to mass delete all of them).

  1. global class deleteAccounts implements Database.Batchable  
  2. {  
  3. global final String Query;  
  4. global deleteAccounts(String q)  
  5. {  
  6. Query=q;  
  7. }  
  8.   
  9. global Database.QueryLocator start(Database.BatchableContext BC)  
  10. {  
  11. return Database.getQueryLocator(query);  
  12. }  
  13.   
  14. global void execute(Database.BatchableContext BC,List scope)  
  15. {  
  16. List <Account> lstAccount = new list<Account>();  
  17. for(Sobject s : scope)  
  18. {  
  19.  Account a = (Account)s;  
  20. lstAccount.add(a);  
  21. }  
  22. Delete lstAccount;  
  23. }  
  24.   
  25. global void finish(Database.BatchableContext BC)  
  26. {  
  27.                 //Send an email to the User after your batch completes  
  28.                 Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();  
  29. String[] toAddresses = new String[] {‘sforce2009@gmail.com’};  
  30. mail.setToAddresses(toAddresses);  
  31. mail.setSubject('Apex Batch Job is done‘);  
  32. mail.setPlainTextBody('The batch Apex job processed ');  
  33. Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });  
  34. }  
  35. }  


This is how the batch class is called

  1. id batchinstanceid = database.executeBatch(new deleteAccounts(‘select Id from Account’));  

When you instantiate the global class and called it using database.executeBatch, the process gets started. As you have observed the deleteAccounts class accepts your query as a parameter in the constructor and sets it to the string variable called Query.
The start method of deleteAccount class which extends database.batchable interface sets the current query to execute using the Database.getQueryLocator method.
Then the result of the query can be captured in execute method. The scope list of SObjects returned as the result of your query.
When you are executing your batch with a query which returns thousands of records, the batch will be executed with 200 records each time that is salesforce divides the total number of records in to batches. Each batch contains 200 records by default (though this is configurable less than 200 by just introducing the number when you are calling the batch class like database.executebatch(new deleteAccounts(‘your query’), number here);).
After processing each batch, the governor limits are reset.
Once the whole batch of thousands records are done the Finish method gets called and an email will be sent to the specified person.
==========================================
Calling one batch class in another batch class
=====================================================
global class batchApexClass implements Database.Batchable<sObject>{
  global final String query;
  public batchApexClass(){
    query='select name from Studant__c';
  }
  
  // this method retrive all the records from specified object
  global  Database.QueryLocator start(Database.BatchableContext BC){
   return Database.getQueryLocator(query);
  }
  global void execute(Database.BatchableContext BC,List<Studant__c> scope){
   List<Studant__c> li=new List<Studant__c>();
    for(sObject s:scope){
     Studant__c std=(Studant__c)s;
     std.name='sunil';
     
     li.add(std);
    }
    update li;
  }
  global void finish(Database.BatchableContext BC){
          //Send an email to the User after your batch completes
                Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
String[] toAddresses = new String[] {'practice.sfdc@gmail.com'};
mail.setToAddresses(toAddresses);
mail.setSubject('Apex Batch Job is done');
mail.setPlainTextBody('oyeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ');
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
  }
}


USING QUERY LOCATOR

global class batchApexClass implements Database.Batchable<sObject>{
  global final String query;
  public batchApexClass(){
    query='select name from Studant__c ';
  }  
  // this method retrive all the records from specified object
  global  Database.QueryLocator start(Database.BatchableContext BC){
   return Database.getQueryLocator(query);
  }
  global void execute(Database.BatchableContext BC,List<Studant__c> scope){
   List<Studant__c> li=new List<Studant__c>();
    for(sObject s:scope){
     Studant__c std=(Studant__c)s;
     std.name='student update';
    
     
     li.add(std);
    }
    update li;
  }
  global void finish(Database.BatchableContext BC){
 database.executeBatch(new batchApexClass1 ());

  }
}
=========================================
Developer console code
=========================================
batchApexClass  b = new batchApexClass ();
database.executeBatch(b);


global class scheduleExampleBatchClass implements Schedulable{
global void execute(Schedulable ctx){
ExampleBatchClass ebc = new ExampleBatchClass();

}
}

=======================================

Run schedule class for Developer console
System,schedule('wt','59 * * * * ?',new scheduleExampleBatchClass);

=======================================


USING ITERABLE
global class ExampleClass implements Database.Batchable<batch__c>
{
global Iterable<batch__c>start(Database.BatchableContext BC)
{
List<batch__c> b = [SELECT name,ID from batch__c];
return b;
}
global void execute(Database.BatchableContext BC,List<batch__c>bat){
{
for(batch__c b:bat){
b.name = 'Wt Test';
}
update bat;
}
global void finish(Database.BatchableContext BC){
System.debug('Success');

}

}



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