The creation.cs file has the code that is run on creation. code in update.cs is always run (create/update). The code in save is always run (create/update).

Create.cs

namespace DBI.Synchronization.Processing.ServiceManagement.Tasks
{
    internal static class ActivityExtensions
    {
        internal static SMTask CreateChild(this long parentId, SMWorkOrderTaskTypeEnum type)
        {
            var parent = SMTaskFactory.Factory.Fetch(parentId);
            var child = parent.AddChildTask();
            child.TaskType = type;
            child.Parent = parent;
            child.WorkOrderObject = parent.WorkOrderObject;
            child.WorkTypeDbKey = child.WorkOrderItemObject.WorkTypeDbKey = parent.WorkTypeDbKey;
            child.DepartmentDbKey = child.WorkOrderItemObject.DepartmentDbKey = parent.DepartmentDbKey;
            child.SMSaleLocationID = child.WorkOrderItemObject.SMSaleLocationID = parent.SMSaleLocationID;
            child.RateSheet = child.WorkOrderItemObject.RateSheet = parent.RateSheet;
            child.SMTechnicianID = parent.SMTechnicianID;
            child.TaskSourceTypeEnum = parent.TaskSourceTypeEnum;
            child.JobCostingTypeEnum = child.WorkOrderItemObject.JobCostingTypeEnum = parent.JobCostingTypeEnum;
            child.SMAgreementServiceDbKey = child.WorkOrderItemObject.SMAgreementServiceDbKey = parent.SMAgreementServiceDbKey;
            // prefill job
            if (child.IsFlatRate())
                PrefillJob(parent.WorkOrderObject.JCJob, child.FlatRateLaborRevenueWorkOrderItemObject, child.FlatRatePartsRevenueWorkOrderItemObject);
            else
                PrefillJob(parent.WorkOrderObject.JCJob, child.WorkOrderItemObject);

            child.WorkOrderItemObject.PrefillTaxInformation();
            child.WorkOrderItemObject.PrefillProduct();

            return child;
        }

        internal static void PrefillJob(Sage.Accounting.ProjectCosting.IPCProjectItem job, params SMWorkOrderItem[] items)
        {
            if (items == null || items.Length == 0)
                return;

            foreach (var item in items)
            {
                item.PCProjectItemDbKey = DbKey.Null;
                item.JCJob = job;
            }
        }

        internal static void PrefillTaxInformation(this SMWorkOrderItem item)
        {
            if (item.SYSTaxStatusDbKey.ToLong() == null)
                item.PrefillTaxFields();
        }

        static T GetByLocation<T>(SaleLocationEnum location, Func<T> center, Func<T> site)
        {
            return (location == SaleLocationEnum.ServiceCenter) ? center() : site();
        }

        internal static void PrefillProduct(this SMWorkOrderItem item)
        {
            if (item.ProductDbKey.ToLong() == null)
                item.ProductDbKey = GetProduct(item);
        }

        static DbKey GetProduct(SMWorkOrderItem item)
        {
            var type = (SMWorkOrderTaskTypeEnum)item.SMWorkOrderItemTypeDbKey.ToLong().Value;
            switch (type)
            {
                case SMWorkOrderTaskTypeEnum.FlatRateLaborRevenue:
                    return item.WorkTypeObject.FlatRateLaborProductDbKey;
                case SMWorkOrderTaskTypeEnum.FlatRatePartsRevenue:
                    return item.WorkTypeObject.FlatRatePartsProductDbKey;
                case SMWorkOrderTaskTypeEnum.Labor:
                    return item.WorkTypeObject.LaborProductDbKey;
                case SMWorkOrderTaskTypeEnum.Miscellaneous:
                    return (item.SMMiscellaneousItemDbKey.ToLong() == null || item.MiscellaneousItem.ProductDbKey.ToLong() == null)
                        ? item.WorkTypeObject.MiscellaneousProductDbKey
                        : item.MiscellaneousItem.ProductDbKey;
                case SMWorkOrderTaskTypeEnum.Parts:
                    return item.WorkTypeObject.PartsProductDbKey;
                default:
                    return DbKey.Null;
            }
        }
    }
}

Save.cs

public void Persist(SMTask entity)
{
    using (var rootTransaction = new PersistentObjectTransaction(entity, Sage.ObjectStore.Builder.TransactionMode.Required))
    {
        // update to make sure we have task id

        entity.Update();

        if (entity.TaskType == SMWorkOrderTaskTypeEnum.FlatRate)
        {
            PersistItem(entity, entity.FlatRateLaborRevenueWorkOrderItemObject);
            PersistItem(entity, entity.FlatRatePartsRevenueWorkOrderItemObject);
        }

        if (entity.SMWorkOrderDbKey.ToLong().HasValue && TASKS_WITH_ITEM.Contains(entity.TaskType))
        {
            PersistItem(entity, entity.WorkOrderItemObject);
        }

        entity.Update();
        rootTransaction.Commit();
    }
}


void PersistItem(SMTask task, SMWorkOrderItem item)
{
    using (var transaction = new PersistentObjectTransaction(item, Sage.ObjectStore.Builder.TransactionMode.Required))
    {
        item.AssociatedTask = task;
        if (item.SMWorkOrderDbKey.ToLong() == null)
            item.SMWorkOrderDbKey = task.SMWorkOrderDbKey;

        PrefillWorkOrderItemFields(item);
        item.PrefillTaxInformation();
        if (item.WorkOrderItemType == SMWorkOrderTaskTypeEnum.Labor)
            item.UnitCost = item.CalculateLaborUnitCost(item.Technician, item.PayTypeObject);

        item.Update(false);

        transaction.Commit();
    }

    task.WorkOrderItemDbKey = item.SMWorkOrderItemID;
}

private void PrefillWorkOrderItemFields(SMWorkOrderItem item)
{
    var task = item.AssociatedTask;

    if (task.WorkTypeDbKey.ToLong() == null)
        task.WorkTypeDbKey = task.ParentTaskObject.WorkTypeDbKey;

    item.PrefillProduct();
}

Update.cs

public void Map(LaborActivityDTO source, SMTask target)
{
    var item = target.WorkOrderItemObject;
    item.WorkOrderItemType = SMWorkOrderTaskTypeEnum.Labor;
                
    item.PayTypeDbKey = source.PayTypeId.ToDbKey();
    target.SMTechnicianID = item.SMTechnicianDbKey = source.TechnicianId.ToDbKey();
    target.CostQuantity = item.CostQuantity = source.UnitCostQuantity;
    target.UnitCost = item.UnitCost = source.UnitCostRate;
    target.BilledQuantity = item.BilledQuantity = source.UnitBilledQuantity;
    target.UnitSale = item.UnitSale = source.UnitBilledRate;
    target.ServiceLocationEquipmentDbKey = item.ServiceLocationEquipmentDbKey = source.EquipmentId.ToDbKey();

    item.SYSTaxGroupDbKey = source.TaxGroupId.ToDbKey();
    item.SYSTaxStatusDbKey = source.TaxStatusId.ToDbKey();

    if (source.CompletionDate.HasValue)
    {
        item.Completed = true;
        item.AccountingDateTime = source.CompletionDate.GetValueOrDefault();
    }
    else
    {
        item.Completed = false;
    }

    var repairCodeId = source.RepairCodeId.ToDbKey();

    if (repairCodeId != item.SMRepairCodeDbKey)
    {
        item.SMRepairCodeDbKey = repairCodeId;
        item.PrefillCostCodeAndCategory();
    }

    target.Description = item.Description = source.Description ?? (item.RepairCode != null ? item.RepairCode.Description : "");
}