Q: How to sequentially resolve QDefer?

[digitalaspirin]

I would appreciate your opinion on the following problem

The user retrieves from a backend a list of items and he is given the option to select a bunch of them and place a request to delete them. However, the backend interface only supports single delete requests. That is delete(id0) delete(id1) and so forth.

What is the best approach of crafting a method so that upon receiving a reply, resolve the QDefer object, and only then place a delete request for next pending item in the queue?

Currently I have approached it as follows:

connect(this,&MyList::deleteItem, this, &MyList::onDeleteItem, Qt::QueuedConnection);

… at some point the user clicks to delete selected items and deleteItem signal is fired…
m_itemsForDeletion = Qvector<int>{1,2,3,4,5};
emit delete();

QDeferred<Qstring> requestDelete(qint32 item)
{
	QDeferred<Qstring> retDeferred;
	… requestToDelete(item); //transaction with backend
	... wait for reply and resolve() or reject()
	retDeferred.resolve(“”);

	return retDeferred;
}

void MyList::onDeleteItem()
{
    if (m_itemsForDeletion.size()>0) {
        auto item = m_itemsForDeletion.takeFirst();
        requestDelete(item)
        .fail([](QString msg) {
             displayErrorMessage(msg);
         })
        .done([this](QString) {
             emit delete(); // keep emitting signal until all items have been deleted.
         });
    }

}

[juangburgos]

If you have no limit on the simultaneauos number of delete requests, I'd just fire them up all at once and use the when method to know when all are done (see here).

If you have limits, then one option is to have a queue of delete requests and dispatch them one at a time.

[digitalaspirin]

Thanks for your reply,
I'll have to dispatch the requests one at a time.

PS: Great lib BTW.