with

let getGraphChecklistById = Promise.coroutine(function*(pId) {
    console.log('> getGraphChecklistById()');

    let checklist = yield getChecklistById(pId);
    checklist.__node__ChecklistItemGroups = yield fetchChecklistItemGroupsByChecklistId(pId); // Returns a promise.
    for (let pItem of checklist.__node__ChecklistItemGroups) {
        pItem.__node__ChecklistItems = yield fetchChecklistItemsByXrefId(pItem.xchlclig_id);
    }
    return checklist;
});