gistfile1.txt

trigger CountIncidents on itil_b__Incident__c (after insert, after update){
    List<Id> AccountIDs = itil_b.Util.getIDFields(Trigger.new,'itil_b__account__c');

    List<AggregateResult> totalIncidents = [SELECT itil_b__Account__c, COUNT(Id)
    FROM itil_b__Incident__c WHERE itil_b__Account__c IN :AccountIDs AND itil_b__Account__c != null
    GROUP BY ROLLUP(itil_b__Account__c)];

    Map<id,Account> accounts = new Map<id,Account>([SELECT total_incidents__c, id FROM Account WHERE Id IN :accountIDs]);

    for(AggregateResult ar: totalIncidents){
        Id accountId = (id) ar.get('itil_b__Account__c');
        if(accountId == null)
            continue; //this aggregate result isn't for a specific account, skip it.
        Integer incidentCount = (Integer) ar.get('expr0');
        Account a = accounts.get(accountId);
        a.total_incidents__c = incidentCount;
    }

    update accounts.values();
}