How to keep state of static variables in Apex Batch Jobs - salesforce

Question

I have to execute many(more than 10) batch jobs one after other to make sure it doesn't exceeds governor limits.
I want to implements something like below but it doesn't work because stateful doesn't work for static.
public class MyBatch implements Database.Batchable<SObject>,
Database.Stateful
{
private String a;
private Static List<String> aList = new List<String>();
private static Integer currentIndex = 0;
static
{
aList = getAllAList();
}
public MyBatch(String a)
{
this.a = a;
}
public Database.QueryLocator start(Database.BatchableContext bc)
{
return Database.getQueryLocator('some query which may get 30k
records');
}
public void execute(Database.BatchableContext BC, List<sObject>
recordList)
{
System.debug('execute');
System.debug(recordList);
}
public void finish(Database.BatchableContext BC)
{
System.debug('finish');
//do I have another A.
if(currentIndex < aList.size())
{
cuurentIndex++;
System.debug('Starting another batch: '+ anotherA);
Database.executeBatch(new MyBatch(aList.get(currentIndex));
}
}
}
So here in finish method, currentIndex is always zero and because of that it always get first value in aList.
I also tried with some other static variables from other class as well but that also doesn't work.
Is there any way to achieve this thing without using database transactions?

Answer 1

You can't call it like this because the finish method is just called once at the end of (all) batches.
So the start and the execute method are important. Depending on the batchsize the query result will be devided into x chunks and the execute method will do the rest.
And since the finish method is just called once your index will be increment at the most once. If you increment it in the excute method it will increment each time a new batch(chunk) run

Answer 2

I have implemented through keeping currentIndex in batch class and passing it when calling next batch.
public class MyBatch implements Database.Batchable<SObject>,
Database.Stateful
{
private List<String> aList = null;
private Integer currentIndex;
public MyBatch(List<String> aList, Integer index)
{
this.aList = aList;
this.index = index;
}
public Database.QueryLocator start(Database.BatchableContext bc)
{
return Database.getQueryLocator('some query which may get 30k
records');
}
public void execute(Database.BatchableContext BC, List<sObject>
recordList)
{
System.debug('execute');
System.debug(recordList);
}
public void finish(Database.BatchableContext BC)
{
System.debug('finish');
//do I have another A.
currentIndex++;
if(currentIndex < aList.size())
{
System.debug('Starting another batch: ');
Database.executeBatch(new MyBatch(aList, currentIndex);
}
}
}
So idea here is to keep index to batch as private member not as static and check if size doesn't exceed then trigger next batch.