* It is
a powerful new feature to do batch processing on our database records.
* It was released in summer'09.
* It is used to execute large volumes of data unlike ordinary DML and SOQL statements.
* Tasks that require processing of large data
volumes without any active human intervention can take advantage of this
feature.
* As an example, consider the task of validating
addresses in your contacts when you can potentially have millions of contact
records. A batch job would be ideal for this scenario since you can start
the batch job, continue to work or even log off while the job continues to
execute.
* Batch-apex can execute large volumes of data up to 50 million records.
*To remove custom object records in bulk we need to delete it through data loader, now we can do it with Batch-apex.
*For
Mass updating, inserting and other similar scenarios like this can be more
conveniently handled with force.com's Batch Apex.
* With
Batch Apex, we can now build complex, long-running processes on the platform.
This feature is very useful for time to time data cleansing, archiving or data
quality improvement operations.
* To
use this functionality, you need to implement the Database.Batchable interface.
* 'Database' is a class and 'Batchable' is the interface inside the class.
* 'Database' is a class and 'Batchable' is the interface inside the class.
* This
interface demands for three methods to be implemented:
1. Start()
2. execute()
3. finish()
***********
1. Start() Method:
* Start()
method is called at the beginning of a batch Apex job.
* Use this method to
collect the records (of objects) to be passed to the "execute" method
for processing.
* The
start() method determines the set of records that will be processed by the
executeBatch method. We would need to construct a SOQL query and return a
QueryLocator object.
return Database.getQueryLocator( 'SELECT
Name, MailingAddress FROM Contact');
*QueryLocator can retrieve up to 50 million records at a time.
*Instead of QueryLocator, we can use 'Iterable' which can process up to 50 thousand records.
* The Apex engine automatically breaks the massive numbers of records we selected into smaller batches and repeatedly calls the "execute" method until all records are processed.
* Start() and finish() methods executes only one time.
* But execute() method execute many times based on number of batches.
* We can perform all the DML operations here on bulk volumes of data.
*************
**************
Program to give 20% discount on all the books
****************************************
http://salesforcesource.blogspot.in/2010/02/utilizing-power-of-batch-apex-and-async.html
*Instead of QueryLocator, we can use 'Iterable' which can process up to 50 thousand records.
* The Apex engine automatically breaks the massive numbers of records we selected into smaller batches and repeatedly calls the "execute" method until all records are processed.
* Start() and finish() methods executes only one time.
* But execute() method execute many times based on number of batches.
2. execute() Method:
* It will fetch the records from the start method.* We can perform all the DML operations here on bulk volumes of data.
3. finish() Method:
* All the post processing operations like sending emails will be done here. *************
Database.BatchableContext:
* It is the interface which holds the run-time information.**************
Program to give 20% discount on all the books
//To provide 20% discount for all the books /*BatchApexProcessing b = new BatchApexProcessing(); Id jobid = Database.executeBatch(b,3);*/ //Note: If there are any triggers for the object which we are using for
the batchApexProcessing, it won't work //For the below class we are using list, so it can accept upto 50000 records //Database is the class name and Batchable is the interface name which is inside
database class
//To access interface Database.Batchable we have to use
/*
global class BatchApexProcessing implements Database.Batchable<Book__c> {
global Iterable<Book__c> start(Database.BatchableContext bc){
List <Book__c> bl = new List <Book__c>();
bl = [select Id,Name,Author__c,Price__c from Book__c];
return bl;
}
global void execute(Database.BatchableContext bc, LIST<Book__c> bl) {
for(Book__c b:bl) {
b.Price__c *= 0.80;
}
update bl;
}
global void finish(Database.BatchableContext bc) {
}
}
*/
// ******** Using Query Locater ****************
//For the below class we are using Query Locater, so it can accept upto 50 million records
global class BatchApexProcessing implements Database.Batchable<sObject>,Database.stateful {
//database.stateful is used to make data members with new values assigned should reflect
String myname = 'SRINU';
global Database.QueryLocator <Book__c> start(Database.BatchableContext bc) {
myname = 'SRINIVAS';
System.Debug('***** My Name in Start *****'+myname);
List <Book__c> bl = new List <Book__c>();
String Query = 'select Id,Name,Author__c,Price__c from Book__C';
return Database.getQueryLocator(Query);
}
global void execute(Database.BatchableContext bc, LIST<book__c> bl){
for(Book__c b:bl) {
System.Debug('***** My Name in Start *****'+myname);
b.Price__c *= 0.75;
}
update bl;
}
global void finish(Database.BatchableContext bc) {
System.Debug('***** My Name in Start *****'+myname);
}
}
****************************************
http://salesforcesource.blogspot.in/2010/02/utilizing-power-of-batch-apex-and-async.html
