13Mar/1324

Preview of the new Managed Client for Windows Azure Mobile Services

Note: This is my personal blog. Although I’m currently doing an internship at Microsoft and this post is about a product released by Microsoft I worked on, the opinions on this blog are my own. They do not represent the opinions of Microsoft in any way.

Update: Carlos Figueira has a detailed list of breaking changes at his blog.

Update 2: We published an update to fix the issues with Windows Phone 7.5. The update can be found here.

Today we are releasing a pre-release version of the new Managed Client for Windows Azure Mobile Services on NuGet. This release adds several new features and also adds support for Windows Phone 7.5.

The managed client now supports the following platforms:

  • Windows 8
  • Windows Phone 8
  • Windows Phone 7.5
  • Portable class libraries.

Windows Phone 7.5 support and Portable Class Libraries have been among the top requested features by our customers!

uservoice

Great! How do I get it?

The preview is available as a pre-release NuGet package. To use the package you need at least NuGet 2.1.

Note: This version is not officially supported. The latest officially supported client is available as a stable NuGet package or as an extensions sdk.

nuget-pre

To be able to see the package in Visual Studio you need NuGet 2.1 and you need to explicitly tell Visual Studio to show you pre-release packages.

includepre

New features

Beside support for new platforms and bug fixes, this release also adds a bunch of new features:

  • Enum support. Enum types are now supported in queries and for serialization. Enums will be serialized automatically into strings by the client. If for some reason you want to serialize enums as integers, you can still use the following technique to expose the enum as int for serialization.
[JsonProperty("value")]
public int ValueInt { get; set; }

[JsonIgnore]
public EnumType Value { get; set; }
  • Nullable types. Nullable types are now fully supported for queries and serialization. You can read more about Nullable Types here.
  • Contains support in queries. We already supported string.Contains in queries, but now you can also write Contains queries on lists. These queries will now automatically be translated into a sequence of “or” statements:
List names = new List() { "John", "Tom" };
from p in table
where names.Contains(p.Name)
select p
  • MobileServiceCollection. We added a new collection that replaces our previous MobileServiceCollectionView. This class had some problems and was less portable going forward. You can read more about the new collection further on.
  • HttpMessageHandlers. Service Filters available in our previous release are now replaced by HttpMessageHandlers. These classes are part of the recently released HttpClient library and are reusable by everything that uses HttpClient. More on this also further on.
  • Improved unit-testability. We removed the sealed keyword from most of the public facing classes and added interfaces for some of them. This heavily improves the unit testability of the library for us and make it easier for developers to substitute our classes for mocks.

Portable Class libraries

Currently we have separate clients for Windows and Windows Phone 8. This release unifies these platforms by moving towards a Portable Class Library. Portable Class Libraries offer several advantages for developers, since they can now share their codebases using Mobile Services more easily between the different platforms. Also it allows us to rollout changes faster and brings consistency across the supported platforms. You can read more about Portable Class Libraries on MSDN.

Our portable library targets:

  • Windows Store apps
  • Windows Phone 7.5 and higher
  • .Net 4.5
  • Silverlight 4 and higher

This does not mean we support all these platforms. The Portable Class Library need a platform extension assembly to work correctly and it won’t work without it. We only provide platform extension assemblies for Windows Phone 7.5, Windows Phone 8 and Windows Store apps. If you need to support other platforms, you can get the source code from GitHub. More on platform extension assemblies further on. We are considering adding .Net 4.5 support in the future.

Architecture

Although Portable Class Libraries are a great addition to the Managed Mobile Services client, we cannot move all of our code into the Portable Class Library. Some functionality is only available on one platform and other functionality differs between platforms. Therefore, to be able to use the new Managed Client you also need a platform specific assembly, which contains code to be able to use features available on that specific platform. UI authentication is an example of a feature that works different on different platforms and is not portable.

diagram

The design of the managed client is roughly as shown in the diagram. For you as a developer this means you need two assemblies for your Windows Store app to use Mobile Services. For Windows Phone this works a little different. For Windows Phone there is an additional assembly. This assembly contains functionality which is not allowed in background agents. In our case that means that login functionality involving UI lives there. So, if you install this package into a background agent project, make sure to remove the reference to Microsoft.WindowsAzure.Mobile.UI.dll.

With the platform extension assemblies we take an approach similar to what the Reactive Extensions team earlier did with Rx 2.0. We are constantly evaluating what platforms to support with our Portable Class Library with respect to the functionality we can actually put in the portable part, because support for more platforms in general means we have to move more functionality to the platform extension assemblies.

A new collection

MobileServiceCollection is our new collection type that replaces MobileServiceCollectionView going forward. The functionality it offers is similar to its predecessor and it offers more extensibility.

  • Support for paging. Simply give the collection a page size as part of the constructor and it will request the data in batches.
  • Client-side LINQ queries. We acknowledge that OData does not cover all query scenarios for users. To make this as easy as possible you can specify a custom selector function over the data after it has been retrieved from the server. This can be useful for example to wrap your Model objects into a ViewModel before insertion or to do grouping.
  • ISupportIncrementalLoading for Windows Store apps. Some controls in the Windows Runtime support an interface called ISupportIncrementalLoading. This interface allows controls to request extra data when the user scrolls. We have built-in support for this interface for Windows Store apps. Our windows store extension assembly contains the MobileServiceIncrementalLoadingCollection which automatically handles the calls from the controls.

To use the new collection you can simply use our ToCollection() extension methods on IMobileServiceTableQuery<T> and IMobileServiceTable<T> or use on of the available constructors for more customizability.

To actually load data you have to call LoadMoreItemsAsync(). When you have specified a page size before, the collection will only retrieve so much items as you specified, otherwise it will just send the original query to the server. Make sure you always await the calls to LoadMoreItemsAsync and wrap it with a try { } catch { } to handle any exceptions from the server.

MobileServiceCollection<TodoItem, TodoItem> collection = await client.GetTable().ToCollectionAsync();

or with page size 10:

MobileServiceCollection<TodoItem, TodoItem> collection = await client.GetTable().ToCollectionAsync(10);

Note that to load more pages you have to call LoadMoreItemsAsync() yourself.
If you want to do paging in a Windows Store app, you can also use the MobileServiceIncrementalLoadingCollection<TTable, TCol> which implements ISupportIncrementalLoading. For this class you cannot specify a page size since the controls automatically request a number of items. You also do not need to call LoadMoreItemsAsync() since the control will call this method for you.

If you want to do paging on a platform other than the Windows Store you currently don’t have ISupportIncrementalLoading. Instead you have to wire this up yourself. For Windows Phone you can use Scroll Compression states and call LoadMoreItemsAsync yourself.

HttpClient

In this release we are replacing Service Filters, on the Managed C# client, with HttpMessageHandlers which are part of HttpClient. HttpClient offers several advantages over our previous implementation and HttpMessageHandlers allow developers to reuse their handlers for other projects using HttpClient.

ServiceFilters can be easily transformed into HttpMessageHandlers. Consider the following filter created by Josh Twist:

public class BusyServiceFilter : IServiceFilter
{
	private int _callCount = 0;
	private Action _busyIndicator;

	public BusyServiceFilter(Action busyIndicator)
	{
		_busyIndicator = busyIndicator;
	}

	public IAsyncOperation Handle(IServiceFilterRequest request, IServiceFilterContinuation continuation)
	{
		return HandleAsync(request, continuation).
			  AsAsyncOperation();
	}

	private async Task HandleAsync(IServiceFilterRequest request, IServiceFilterContinuation continuation)
	{
		// update the count by one in a single atomic operation. 
		// If we get a 1 back, we know we just went 'busy'
		var outgoingCount = Interlocked.Increment(ref _callCount);
		if (outgoingCount == 1)
		{
			_busyIndicator(true);
		}

		IServiceFilterResponse response = await continuation.Handle(
			request).AsTask();

		// decrement the count by one in a single atomic operation.
		// If we get a 0 back, we know we just went 'idle'
		var incomingCount = Interlocked.Decrement(ref _callCount);
		if (incomingCount == 0)
		{
			_busyIndicator(false);
		}

		return response;
	}
}

This filter creates a busy indicator based on in-flight requests. It can be easy transformed into an HttpMessageHandler. The following sample show an HttpMessageHandler which does the same. Custom HttpMessagehandlers should in most cases derive from DelegatingHandler as they are meant to be “pass-through”.

public class BusyHandler : DelegatingHandler
{
	private int _callCount = 0;
	private Action _busyIndicator;

	public BusyHandler(Action busyIndicator)
	{
		_busyIndicator = busyIndicator;
	}

	protected override async Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
	{
		// update the count by one in a single atomic operation. 
		// If we get a 1 back, we know we just went 'busy'
		var outgoingCount = Interlocked.Increment(ref _callCount);
		if (outgoingCount == 1)
		{
			_busyIndicator(true);
		}

		HttpResponseMessage response = await base.SendAsync(request, cancellationToken);

		// decrement the count by one in a single atomic operation.
		// If we get a 0 back, we know we just went 'idle'
		var incomingCount = Interlocked.Decrement(ref _callCount);
		if (incomingCount == 0)
		{
			_busyIndicator(false);
		}

		return response;
	}
}

Breaking Changes

The switch to HttpClient, the Portable Class Library and the new collection are breaking changes compared to our previous client, but we believe they all benefit developers.

Other breaking changes we made include a switch to Json.NET. While we did our best to keep the behavior the same, there are small changes that could affect you. Most of them actually make your life easier. For example Uri instances can now be serialized without a custom converter.

We also fail early when you try to send numbers, such as longs, ulongs and decimals, to the server which can’t be handled by the server because the number is too large or needs too much precision. As most of you will know, our server runtime is running on JavaScript, in which every number is a double. This means for example you can’t send a long to the server which is greater than 2^53.

exception

Our behavior with multiple calls to Skip(int) and Take(int) has also changed. Multiple Skip calls will now add up, so Skip(10).Skip(8) will result in Skip(18). Multiple calls to Take(int) will result in the lowest being used, so Take(2).Take(30) will result in Take(2). This makes our API consistent with other OData client libraries such WCF Data Services.

More about breaking changes here.

Pre-release

As mentioned before, this is a pre-release of our new library. Things are likely to change between now and the stable release, although we always try to keep the public changes at a minimum. We do NOT recommend the use of this library if you have critical business depending on it, as it is likely to have bugs and is not officially supported.

This release is meant for testing purposes and for us to get feedback on the changes we made. Try it out if you have the chance and submit your feedback and bugs via the forums!

NuGet

This pre-release client is only available on NuGet. Did I already mention you need NuGet 2.1 for it to work? Otherwise Portable Class Libraries and Windows Phone 8 won’t work. If you receive errors such as:

6507_NuGetFailedNeedsUpdate_thumb_3C41099C

Then you need to update your NuGet version via Tools -> Extensions and Updates.

8662_ExtensionsAndUpdates-2_thumb_3BD4D6A7

What’s next?

We plan to update the NuGet package regularly with the latest bug fixes and improvements. Stay tuned for more things to come in the months ahead!

Johan Laanstra (SDE Intern, Windows Azure Mobile Services)

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