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**Note- Not more 5 queued or Active Batch Jobs can be there at a time.
What is the Use of Batch Apex ? Several Apex Governor limits can be conquered using batch apex as it break downs a Job in smaller jobs. It is useful when you require to query thousand of records and perform DML operations on them without hitting the governor limits.
Example :- Suppose you organization has millions of Accounts and you want to update them.
Issues without Batch Apex: How to query records more than 50000 ?
How to perform DML on more than 10000 records?
Lets now see how we overcome it using Batch Apex.
Batch Apex will break down this task into smaller jobs and process them seperately to avoid hitting governor limits. Batch Apex Implements the "Database.Batchable" Interface which has 3 methods.
1. Start
2. execute
3. Finish
2. execute
3. Finish
Start method is First method called automatically when the batch job is invoked. It generates the set of records on which the operation has to be performed and sends it to Execute method in smaller chunks.
Execute Method performs operation which we want to perform on the records fetched from start method.
Finish method is called after processing all the batches in execute method.
Sample Code to Update all Account records using Batch Apex global class AccountUpdatebatch implements Database.Batchable<sObject> {
global Database.QueryLocator start(Database.BatchableContext BC) {
String query = 'SELECT Name FROM Account';
return Database.getQueryLocator(query);
}
global void execute(Database.BatchableContext BC, List<Account> scope) {
//Scope comes from start in batches of 200
for(Account acc : scope)
{
// Write the Operation logic you want to perform here,
// For example I have appended Updated with the account names.
acc.Name = acc.Name + '-Updated';
}
update scope;
}
global void finish(Database.BatchableContext BC) {
// Write the Operation logic you want to perform after all Batches are processed.
}
}
To Run the Batch Apex : Go to console and run the below mentioned code snippet .
AccountUpdatebatch bat= new AccountUpdatebatch ();
database.executebatch(bat);
you are doing a great job. keep it up
ReplyDeleteThat is a really nice and simple example...easy to understand for freshers....keep up the good work!
ReplyDeletePlease help me understand difference between querylocator and iterable in batch apex. Thanks in advance.
ReplyDeleteQueryLocator is used when the scope is directly taken from a SOQL :
DeleteUse 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.
Iterable is used 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.
Nice Saurabh, Really great job!.
ReplyDelete