Batch Class : how to get Scope size informations at constructor level

Question

This is a philosophical question (maybe not properly) ... I'm wondering about being able to have informations about the scope size for every batch chunk. OK, it's possibible to get the scope size() within an execute call of the batch, but what if I'd like to have informations about this size at Batch class constructor level? So, when someone call

ID batchprocessid = Database.executeBatch(new myBatch(), x);

could I know, in the batch constructor, the value of x?

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RECAP

1 - JEREMY NOTTINGHAM SOLUTION:

You can set up your constructor to take the batch size as an argument, and then have access to it later, as long as you implement Database.Stateful:

    global class myBatch implements Database.Batchable<sObject>, Database.Stateful
{
    private Integer batchSize;
    global myBatch(Integer batchSize)
    {
        this.batchSize = batchSize;
        system.debug('batch size: ' + this.batchSize);

        //other constructor stuff
    }
    ...
}

Then your call to run the batch looks like this:

ID batchprocessid = Database.executeBatch(new myBatch(x), x);

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1 - MY ANSWER:

I just considered your solution, but my question was a bit harder, i.e. : your solutions works until I know I have to call the myBatch class constructor passing x as parameter, but this way someone else could always call the empty constructor, and I would not be able to catch the scope size.

I would like to be able to do it in any situation , even if someone else call my Batch class constructor (any constructor he wants to call)!

Answer 1

I don't believe that you can.

Instead, consider protecting access to your batcheable class and provide a service class that calls the constructor for you, passing in the batch size, and then you call

global static class myService {
    global static void RunMyBatch(Integer batchSize) {
        myBatch theBatch = new myBatch (batchSize); // Batch size in constructor
        Database.executeBatch(theBatch, batchSize);
    }
}

Answer 2

There are good reasons why the question isn't just philosophical.

I have a batch which must run with scope 100 (any less would affect performance, any more could hit limits and fail). There are a number of ways I can make this scope size available (public final Integer BATCH_SIZE, or a Custom Setting), but there is no way to semantically guarantee it gets used. Like you said, some other developer might try to use my batch without realizing the limit, since there's nothing at compile or run-time (other than the batch executions failing) that tell them it's wrong.

How about this: make the constructor private and force developers to execute the batch via a public static method.

public class MyBatch implements Database.Batchable<Id> {

    public static void executeInstance(Integer batchSize) {
        Database.executeBatch(new MyBatch(), batchSize);
    }

    private MyBatch(){}

    public List<Id> start(Database.BatchableContext bc) {
        ...
    }

    public void execute(Database.BatchableContext bc, List<Id> accIds) {
        ...
    }

    public void finish(Database.BatchableContext bc) {
        ...
    }

}

The private constructor guarantees it cannot be constructed outside of the class, i.e. Database.executeBatch(new MyBatch(), X). The only option available to developers is MyBatch.executeInstance(X), where you can access the value of X (and, in my case, validate it).

Answer 3

Yes, it's possible.

When you call your batch class :

ID batchprocessid = Database.executeBatch(new MyBatch(), x);

You can get the TotalJobItems attribute of the AsyncApexJob object like this :

public class MyBatch implements Database.Batchable<SObject>, Database.AllowsCallouts {

    public database.querylocator start(Database.BatchableContext bc) {
        Id jobId = bc.getJobId();

        List<AsyncApexJob> aaj = [SELECT Id, TotalJobItems FROM AsyncApexJob WHERE Id=:jobId];

        Integer totalJobs = 0;

        if(aaj.size() > 0) {
            totalJobs = aaj[0].TotalJobItems; // The number x you want
        } 
    }
}

Answer 4

You can set up your constructor to take the batch size as an argument, and then have access to it later, as long as you implement Database.Stateful:

global class myBatch implements Database.Batchable<sObject>, Database.Stateful
{
    private Integer batchSize;
    global myBatch(Integer batchSize)
    {
        this.batchSize = batchSize;
        system.debug('batch size: ' + this.batchSize);

        //other constructor stuff
    }
    ...
}

Then your call to run the batch looks like this:

ID batchprocessid = Database.executeBatch(new myBatch(x), x);

Answer 5

It is not possible to get this data in constructor I believe. Can you please share, what are you trying to do with this number of records processed by scope. We might be able to suggest some work around.