Batch Apex in
Salesforce
To use
batch Apex, you must write an Apex class that implements the
Salesforce-provided interface Database.Batchable, and then invoke the class
programmatically.
Start
method
The start method is called at the beginning of a batch Apex job. Use the start method to collect the records or objects to be passed to the interface method execute.
Syntax: global (Database.QueryLocator | Iterable<sObject>) start(Database.BatchableContext bc) {}
This method returns either a Database.QueryLocator object or an
iterable that contains the records or objects being passed into the job.
Execute
Method
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.
Syntax: global void execute(Database.BatchableContext BC, list<P>){}
This method takes
the following:
o A reference to the Database.BatchableContext object.
o 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.
Batches of records
execute in the order they are received from the start method.
Finish Method
Syntax: 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.
Example of Batch Apex Class:
Batch Schedule Class
global class batchContactUpdate implements Database.Batchable<sObject>
{
global Database.QueryLocator start(Database.BatchableContext BC)
{
String query = 'SELECT Id, FirstName,LastName FROM Contact';
return Database.getQueryLocator(query);
}
global void execute(Database.BatchableContext BC, List<Contact> scope)
{
for(Contact a : scope)
{
a.FirstName=a.FirstName+'FirstName is Updated';
a.LastName = a.LastName +'LastName is updated';
}
update scope;
}
global void finish(Database.BatchableContext BC)
{
}
}
Schedule Class
global class BatchScheduleUpdate implements Schedulable
{
global void execute(SchedulableContext sc)
{
// Implement any logic to be scheduled
// We now call the batch class to be scheduled
BatchContactUpdate b = new BatchContactUpdate ();
//Parameters of ExecuteBatch(context,BatchSize)
database.executebatch(b,200);
}
}
Schedule from Developer Console
BatchScheduleUpdate batchSch=new BatchScheduleUpdate();
String sch='0 5 2 * * ?';
//System.schedule(String jobName, String cronExp, APEX_OBJECT schedulable);
System.schedule('Batch Schedule', sch , batchSch);
Hope this will helpful for you...!
Thank you...!
