Using Aggregate SOQL queries/results in Batch Apex

In previous post, we had created a schedulable batch apex that implements Database.Batchable<sObject> in Salesforce, but if you want to use SOQL having aggregate functions like SUM(), MAX(), COUNT() on results grouped by “GROUP BY” clause in start execution, changing to interface Database.Batchable<AggregateResult> isn’t a workable way, because it fails with the below compile error :

Class must implement the global interface method: Iterable<AggregateResult> start(Database.BatchableContext) from Database.Batchable<AggregateResult>

The following sample code will explain this.

To fix this, using Apex classes that implement Iterator<AggregateResult> and Iterable<AggregateResult> seems the only way for now.

Here is the outline what we should do.
1. Create an Apex class implements Iterator<AggregateResult>.
2. Create an Apex class implements Iterable<AggregateResult>.
3. Implementing to Database.Batchable<AggregateResult>, and Using Iterable at start execution in Batch Apex.

Let’s get started.

Iterator Apex class

Create an Apex class named “AggregateResultIterator” with the following source code :

Iterable Apex class

Create an Apex class named “AggregateResultIterable” with the following source code :

Batch Apex

Then implement Batch Apex from Database.Batchable<AggregateResult>, and use Iterable<AggregateResult>, AggregateResultIterable instead of Database.QueryLocator at start execution, as the following source code :

Operation check

Run SampleAggregateBatch and check debug log.

It seems working fine! : )

Enjoy it!