Exchange Web Services: Batching with FindItemsResult<Item>

Question

I'm writing an app to process email attachments, using Exchange Web Services.

The general structure of my problem area is as follows:

public static void Main()
{
    FindItemsResults<Item> findResults = FindItems();

    foreach (Item item in findResults)
    {
        DoSomethingWithItem(item);
    }
}

public static FindItemsResults<Item> FindItems()
{
            FindItemsResults<Item> findResults;

            ItemView view = new ItemView(10);    //batching 10 at a time
            view.OrderBy.Add(ItemSchema.DateTimeReceived, SortDirection.Ascending);
            view.PropertySet = new PropertySet(
                BasePropertySet.IdOnly,
                ItemSchema.Subject,
                ItemSchema.DateTimeReceived);

            findResults = service.FindItems(
                WellKnownFolderName.Inbox,
                new SearchFilter.SearchFilterCollection(
                    LogicalOperator.Or,
                    new SearchFilter.ContainsSubstring(ItemSchema.Subject, Properties.Settings.Default.EmailSubject)),
                view);

            //return set of emails
            return findResults;
}

At first, this looked OK - it processed my earlier test examples perfectly well. But when I start testing with bulk loads, I realised that it was only processing the first 10 items, since I was specifying a batch size of 10 items (ItemView view = new ItemView(10)), but I wasn't checking for further batches.

I could have simply increased the batch size, but a quick google later, I found a better example:

public static FindItemsResults<Item> FindItems()
{
            FindItemsResults<Item> findResults;

            ItemView view = new ItemView(10, 0, OffsetBasePoint.Beginning); 
            view.OrderBy.Add(ItemSchema.DateTimeReceived, SortDirection.Ascending);
            view.PropertySet = new PropertySet(
                BasePropertySet.IdOnly,
                ItemSchema.Subject,
                ItemSchema.DateTimeReceived);

            do
            {
                findResults = service.FindItems(
                    WellKnownFolderName.Inbox,
                    new SearchFilter.SearchFilterCollection(
                        LogicalOperator.Or,
                        new SearchFilter.ContainsSubstring(ItemSchema.Subject, Properties.Settings.Default.EmailSubject)),
                    view);

                //any more batches?
                if (findResults.NextPageOffset.HasValue)
                {
                    view.Offset = findResults.NextPageOffset.Value;
                }
            }
            while (findResults.MoreAvailable);

            return findResults;
}

This loops through as many emails as I care to throw at it, but for reasons I can't yet understand, the foreach loop now only processes the first item in findResults.

Even though findResults contains more than one item (findResults.Items.Count > 1), with my second example, findResults.MoreAvailable = false. Fair enough, I've looped through the batches earlier, so it makes sense that I'm looking at the end of the last batch.

But how do I reset findResults so that it will process the whole lot? I tried setting findResults.MoreAvailable but it is readonly... What am I missing?

CONCLUSION:

OK, so I can either process the items one batch at a time, or I can add each item in each batch to a List and process them later, as I currently do.

There is not a lot between them; I've initially started using a List, but I'll consider the choice further.

Answer 1

It seems to my that your main problem is that you try define a function which returns FindItemsResults<Item>. If you use paring of results you will have not one object of this type. Instead of that on retrieving of every new page the FindItemsResults<Item> will be overwritten. Following example display subjects of all items from the Inbox:

ItemView view = new ItemView(10, 0, OffsetBasePoint.Beginning);
view.OrderBy.Add(ItemSchema.DateTimeReceived, SortDirection.Descending);
view.PropertySet = new PropertySet(
    BasePropertySet.IdOnly,
    ItemSchema.Subject,
    ItemSchema.DateTimeReceived);

// save the folder where we will make searching to do this one time
Folder myInbox = Folder.Bind(service, WellKnownFolderName.Inbox);

FindItemsResults<Item> findResults;

do
{
    findResults = myInbox.FindItems(
        new SearchFilter.ContainsSubstring(ItemSchema.Subject,
                Properties.Settings.Default.EmailSubject)),
        view);

    foreach (Item item in findResults)
    {
        // Do something with the item.
        Console.WriteLine();
        if (item is EmailMessage)
        {
            EmailMessage em = item as EmailMessage;
            Console.WriteLine("Subject: \"{0}\"", em.Subject);
        }
        else if (item is MeetingRequest)
        {
            MeetingRequest mr = item as MeetingRequest;
            Console.WriteLine("Subject: \"{0}\"", mr.Subject);
        }
        else
        {
            // we can handle other item types
        }
    }

    //any more batches?
    if (findResults.NextPageOffset.HasValue)
    {
        view.Offset = findResults.NextPageOffset.Value;
    }
}
while (findResults.MoreAvailable);

The code display the subjects on the console output. If you want to use EmailMessage or MeetingRequest in another way you should modify the code correspondent. You can also define a delegate which do something with the found EmailMessage or MeetingRequest and call the delegate on the place of Console.WriteLine. If you do need to same all items somewhere, then you will have to create some collection like List<Item>, fill there in the function and return instead of FindItemsResults<Item> which you currently do.