BatchUpdateContactMailingCity class to update the contact records

BatchUpdateContactMailingCity.cls

global with sharing class BatchUpdateContactMailingCity implements Database.Batchable<SObject>{
    
    global Database.QueryLocator start(Database.BatchableContext bc){
        String query = 'Select Id, BillingCity,(Select Id,Name, MailingCity from contacts) from Account';
        return Database.getQueryLocator(query);
    }

    global void execute(Database.BatchableContext bc, List<Account> accList){

        //list of contacts to update
        List<Contact> conListToUpdate = new List<Contact>();
        for(Account acc: accList){
            for(Contact con: acc.contacts){
                con.MailingCity = acc.BillingCity;
                conListToUpdate.add(con);
            }
        }
        if(conListToUpdate.size()>0){
            List<Database.SaveResult> updateResults = Database.update(conListToUpdate,false);
            List<SObject> objList = new List<SObject>();
            objList.addAll(conListToUpdate);
            //call generic method to create the error log records
            Util.createError(updateResults,objList,'Contact Update');
        }
    }
    global void finish(Database.BatchableContext bc){
        //add the finish code here
    }
}