System.QueryException: Aggregate query has too many rows for direct assignment, use FOR loop

Question

I am getting this error while running batch class. I am using sub query in query locator.

String SOQL_Query = 'Select id,name,(select id,name from Safety__r) from Study__c where Reference_Date <= TODAY limit 1000';

And in execute method,iterating over returned Study records and putting child records in Map.

for(Study__c study:recs){

     safMap.put(study.id,study.Safety__r); 
   }

for(Study_CELG_IPS__c study:recs){

     flag=false;
     if(safMap.get(study.id).size()==0){
        flag= true;    
    }else{
         safList= safMap.get(study.id);
     }

   //code
}

Answer 1

This problem is related to your query because it contains more then 250 rows.

So you need to separate it into another query. That will solve your problem

As per Salesforce docs

This error happens when you're trying to use an aggregate function (like COUNT) on a query that has too many rows. To fix the error remove this condition:

for (childtype ch : Parent.children) {

//do some logic...

}

Alternatively, have a map of parent to child objects and get the size of each key from the map.

Reference

Reference 2