Salesforce Batch Class for Aggregate Queries

Recently, I got one requirement, in which I have to use aggregate queries in batch apex class. My requirement was totally different. For blog I'm using Account and Contact as a example.
Let us have a walkthrough how to set up Push Notification.

Step 1. Create the Notification Route.

• AggregateResultIterator
• AggregateResultIterable
• Implementing to Database.Batchable
• Iterable start method of Batch Class

AggregateResultIterator

global class AggregateResultIterator implements Iterator<aggregateresult> {
  AggregateResult [] results {get;set;}
  // tracks which result item is returned
  Integer index {get; set;} 
       
  global AggregateResultIterator(String query) {
    index = 0;
    results = Database.query(query);            
  } 

  global boolean hasNext(){ 
    return results != null &amp;&amp; !results.isEmpty() &amp;&amp; index &lt; results.size(); 
  }    

  global AggregateResult next(){        
    return results[index++];            
  }       
}
</aggregateresult>

AggregateResultIterable

global class AggregateResultIterable implements Iterable<aggregateresult> {
  private String query;

  global AggregateResultIterable(String soql){
    query = soql;
  }

  global Iterator<aggregateresult> Iterator(){
    return new AggregateResultIterator(query);
  }
}
</aggregateresult></aggregateresult>

global class BatchSummariseAccountSummary implements Database.Batchable<aggregateresult>{
    global Iterable<aggregateresult> start(Database.BatchableContext BC){
        return new AggregateResultIterable('Select Count(Id) cactive,AccountId  From Contact Where AccountId != null GROUP BY AccountId ORDER BY AccountId DESC');
    }
    global void execute(Database.BatchableContext BC, List<sobject> scope){   
         List<account> lstAccount=new List<account>();
         for(sObject sObj : scope) {
          AggregateResult ar = (AggregateResult)sObj;
          Account acc=new Account();
          //ContactsCount__c is custom field on Account
          acc.ContactsCount__c=Decimal.valueOf(ar.get('cactive')+'')
          lstAccount.add(asum);          
        }
        if(!lstAccount.isEmpty()){                    
            update lstAccount;
        }
    } 
    global void finish(Database.BatchableContext BC){
         
    }
}
</account></account></sobject></aggregateresult></aggregateresult>

Note: After save whole code you can run batch from Developer console with below code

BatchSummariseAccountSummary  bsas=new BatchSummariseAccountSummary();
database.executebatch(bsas); 

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