Can I tell how many records in a Database.QueryLocator()?

Question

According to the documentation, in a batch a Database.QueryLocator can retrieve up to 50 million records.

A maximum of 50 million records can be returned in the Database.QueryLocator object. If more than 50 million records are returned, the batch job is immediately terminated and marked as Failed.

I then cycle through them in batches, default size 200, maximum size 2000. When I run a batch, Salesforce knows how many batches there are, so it must know how many records are in the QueryLocator. But can I find out? The only methods I can see on the QueryLocator are these two:

getQuery() Returns the query used to instantiate the Database.QueryLocator object. This is useful when testing the start method.

iterator() Returns a new instance of a query locator iterator.

I want to know what the total size of the record set is, before I go through all the batches.

Answer 1

Try running a SELECT COUNT() FROM ... query in your start method before calling QueryLocator.

Answer 2

As per the documentation, we do not have any existing functions to get the size.

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_database_batch.htm

You can use the following code to get the total size of returned values:-

global class YourBatchClass implements Database.Batchable<sObject>, Database.Stateful{
global Integer countVariable=0;

global Database.QueryLocator start( Database.BatchableContext BC ) {
    String queryStr =   'select id,name from Contact';
    Database.QueryLocator queryResult= Database.getQueryLocator( queryStr );       
    
    // Get an iterator
    Database.QueryLocatorIterator i =  queryResult.iterator();
    
    // Iterate over the records
    while (i.hasNext())
    {
        countVariable++;
    }
    
    
    system.debug('Total returned Records: '+countVariable);
    return queryResult;
}