I want to create a batch that can update the contact details if it found a contact record
 

• the batch will update the contact record
• will only update the record once

This is my code:


global class AS_UpdateContactFromStagingObject implements Database.Batchable<sObject> {
    global Database.QueryLocator start(Database.BatchableContext BC){
        String query = 'SELECT AS_Contact_Id__c, AS_Pronouns__c, AS_Aboriginal_or_Torres_Strait_Islander__c, AS_Date_of_Birth__c, AS_CALD__c, AS_Vaccination_status__c, AS_Require_an_interpreter__c,   AS_TIS_Interpreter_Language_Required__c, AS_Safe_to_use_this_phone_number__c, AS_Is_it_safe_to_use_this_email_address__c, AS_Can_a_voicemail_be_left__c, AS_Street__c, AS_City__c, AS_State_Province__c, AS_Zip_Postal_Code__c, AS_Country__c, AS_Why_is_this_their_current_location__c, AS_Agency_Referral__c, AS_Contact_Updated__c FROM Contact_Staging__c WHERE AS_Agency_Referral__c = True AND AS_Contact_Updated__c = False';
        return Database.getQueryLocator(query);
    }
    global void execute(Database.BatchableContext BC, List<Contact_Staging__c> batch) {
        System.debug('batch=='+batch);
        List<Contact_Staging__c> conList = new List<Contact_Staging__c>();
        for(Contact_Staging__c a : batch){
            a.AS_Contact_Id__c  = '';
            a.AS_Pronouns__c  = '';
            a.AS_Aboriginal_or_Torres_Strait_Islander__c = '';
            a.AS_Date_of_Birth__c = '';
            a.AS_CALD__c = '';
            a.AS_Vaccination_status__c = '';
            a.AS_Require_an_interpreter__c = '';
            a.AS_TIS_Interpreter_Language_Required__c = '';
            a.AS_Safe_to_use_this_phone_number__c = '';
            a.AS_Is_it_safe_to_use_this_email_address__c = '';
            a.AS_Can_a_voicemail_be_left__c = '';
            a.AS_Street__c = '';
            a.AS_City__c = '';
            a.AS_State_Province__c = '';
            a.AS_Zip_Postal_Code__c = '';
            a.AS_Country__c = '';
            a.AS_Why_is_this_their_current_location__c = '';
            a.AS_Agency_Referral__c = False;
            a.AS_Contact_Updated__c = True;
            conList.add(a);
        }
        update conList;
    }
    global void finish(Database.BatchableContext BC){
    }
}